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KLAIPĖDA UNIVERSITY
DMITRIJ GEROK
GEOLOGICAL STRUCTURE AND SPATIAL DISTRIBUTION
OF PALAEO-INCISIONS IN THE SOUTHEASTERN PART OF
THE BALTIC SEA AND ADJACENT LAND
Doctoral dissertation
Biomedical sciences, ecology and environmental sciences (03B)
Klaipėda, 2015
Dissertation prepared at the Klaipėda University in 2010–2015.
Supervisor – prof. dr. Albertas Bitinas (Klaipėda University;
physical sciences, geology – 05P).
The dissertation will be defended at the Research Board for
ecology and environmental sciences:
Chairman – dr. Nerijus Blažauskas (Klaipėda University, physical
sciences, geology – 05P).
Members:
dr. Sten Suuroja (Geological Survey of Estonia, physical sciences,
geology – 05P);
doc. dr. Zita Rasuolė Gasiūnaitė (Klaipėda University, biomedical
sciences, ecology and environmental sciences – 03B);
doc. dr. Darius Daunys (Klaipėda University, biomedical sciences,
ecology and environmental sciences – 03B);
prof. habil. dr. Sergej Olenin (Klaipėda University, biomedical
sciences, ecology and environmental sciences – 03B).
The defence of dissertation will take place on 26th of November
2015, at 2 p.m., at the Klaipėda University Aula Magna Conference
room.
Address: Herkaus Manto 84, LT-92294, Klaipėda, Lithuania.
The summary of doctoral dissertation sent on 26th of October,
2015.
The dissertation is available at the Library of the Klaipėda
University.
3
CONTENTS 1. INTRODUCTION .......................................................................... 5
2. REVIEW OF PREVIOUS INVESTIGATIONS ........................ 10
2.1 Geological and tectonic settings .............................................. 10
2.1.1 Tectonic settings ................................................................... 10
2.1.2 Stratigraphy .......................................................................... 11
2.1.3 The seismostratigraphic framework ..................................... 15
2.1.4 The sub–Quaternary surface ................................................. 20
2.1.5 Thickness of Quaternary cover ............................................. 22
2.1.6 Geological features of palaeo-incisions ................................ 24
2.2 Overview of previous geophysical activity ............................. 27
2.2.1 Marine continuous seismic reflection profiling (CSP) ......... 27
2.2.2 2D seismic common mid-point (CMP) shooting on land ..... 30
2.2.3 Electrical tomography .......................................................... 32
2.2.4 Gravimetric survey ............................................................... 32
3. MATERIAL AND METHODS ................................................... 34
3.1 Continuous seismic profiling for marine investigations ....... 35
3.2 Geophysical methods for palaeo-incisions survey on land ... 42
3.2.1 The 2D common mid-point (CMP) seismic method ............ 43
3.2.2 Electrical tomography .......................................................... 51
3.2.3 Integration and interpretation of geophysical data ............... 54
3.3 Survey of the sub-Quaternary relief ....................................... 56
3.4 Technique, applied to compose the scheme of palaeo-
incisions ............................................................................................. 57
3.5 Compilation of the pre-Quaternary geological map ............. 62
4. RESULTS ...................................................................................... 63
4.1 The sub-Quaternary relief ....................................................... 63
4.2 Morphology and network of palaeo-incisions ........................ 67
4.3 Infilling of palaeo-incisions ..................................................... 70
4.4 The pre-Quaternary geology ................................................... 76
5. DISCUSSION ................................................................................ 81
5.1 Interpretation of geophysical data .......................................... 81
4
5.2 Geoecological significance of palaeo-incisions ....................... 84
6. CONCLUSIONS ........................................................................... 87
REFERENCES ................................................................................. 89
APPENDIX1 ................................................................................... 100
APPENDIX2 ................................................................................... 106
APPENDIX3 ................................................................................... 109
5
1. INTRODUCTION
Importance of the study. This study contributes to the
understanding of the geological structure of the greater part of the
southeastern Baltic Sea and neighboring land areas. The palaeo-
incisions are widespread in this region. The term palaeo-incision
means a hidden buried valley cutting into the surface of pre-
Quaternary sedimentary bedrock. Palaeo-incisions are generally filled
in by till and glaciofluvial or glaciolacustrine sediments of the
respective glaciations. In general, these structures are exposed within
a wide zone. The outer boundary of this zone coincides with the
extensions of the Pleistocene ice sheets, i.e. the Netherlands,
Denmark, Germany, Poland, Lithuania, Latvia, Estonia, Northwest
Russia and Belarus. They are less common in Scandinavia. In some
areas, e.g. in Lithuania, Latvia and Denmark, they may be related to
river valleys or fracture systems in the pre-glacial bedrock. The terms
palaeo-incision, palaeo-tunnel, tunnel valley, buried valley, palaeo
channel, etc. are used by scientists in different countries.
Studies of palaeo-incisions contribute to a better understanding of
ice sheet dynamics and sedimentation processes during Quaternary
glaciations. The distribution of palaeo-incisions is irregular and
complicated. Thus, the present-day published schemes and maps of
sub-Quaternary surfaces of the southeastern part of the Baltic Sea with
palaeo-incisions are solely indicative. Most schemes and maps are
based on drill-core data, and therefore they contain very little
geophysical information. As the inner structure of palaeo-incisions
differs radically from the surrounding deposits or rocks, geophysical
methods are apt to contain the most appropriate tools for investigation
of their morphology and distribution.
The study area is delimited by the coordinates 55o 20’–56
o 20’ N
and 19o 00’– 22
o 00’E. It is a part of the southeastern part of the Baltic
Sea (Lithuanian offshore and adjacent part of Latvian offshore) and
neighboring land areas.
6
Aims and Objectives. The objective of this work is to study the
extension of the network of palaeo-incisions, to analyze their infillings
and to detail the geological structure of the southeastern part of the
Baltic Sea and adjacent areas on land. The following tasks are
addressed:
1. Re-interpret the previously obtained offshore continuous seismic
profiling data applying modern digital post-processing technique;
2. Interpret the infilling of palaeo-incisions offshore applying both
seismic and well data;
3. Introduce new methods of geophysical prospecting and post-
processing technique for high resolution land investigations of palaeo-
incisions and estimate the effectiveness of the used methods;
4. Compile a set of geological maps of the southeastern Baltic Sea
and adjacent areas on land: a map of palaeo-incisions in the sub-
Quaternary surface and a pre-Quaternary geological map.
5. Compare the newly compiled maps with the results of previous
investigations.
6. Overview the geoecological significance of palaeo-incisions in
the investigated area.
Novelty of the study. This work presents a detailed analysis of
palaeo-incisions applying modern digital technique for interpretation
of seismo-acoustic records made in the southeastern part of the Baltic
Sea. This resulted in the updating of the previous knowledge and
detailing maps of sub-Quaternary relief and pre-Quaternary geology.
These maps specify the previously established geological boundaries
of different geological periods. The map of distribution of the palaeo-
incisions updates the channel system in the southeastern part of the
Baltic Sea and neighboring land areas.
The analysis of palaeo-incisions presents new information on their
infillings.
The new methodological approach includes 2D shallow seismic
profiling and electrical tomography. This combination is used for the
first time to locate palaeo-incisions on land in the western Lithuania.
7
Statements to be defended:
1. Palaeo-incisions are widely distributed in the southeastern part
of the Baltic Sea and form three complicated irregular networks,
differentiated by their morphology and relative depth.
2. Different infillings of the palaeo-incisions are characterized by
an original lithological structure and unique seismic signature. The
identified palaeo-incisions have seven types of internal seismic
reflectors.
3. The application of modern digital technique for the
interpretation of the vintage marine continuous seismic profiling
(CSP) data together with the latest additional CSP data makes it
possible to improve the knowledge of the geological structure of
southeastern part of the Baltic Sea and to compile more detailed maps
of the sub-Quaternary relief and the pre-Quaternary geology.
Scientific approval. The early results of this study have been
presented in two international and three Baltic Sea regional
conferences and seminars:
The 5th scientific-practical conference Marine and Coastal
Researches – 2011, Palanga, Lithuania, April 2011;
IEEE/OES Baltic INTERNATIONAL SYMPOSIUM, Klaipėda,
Lithuania, May 2012;
The 9th Baltic Sea Science Congress 2013, Klaipėda, Lithuania,
August 2012;
The 7th scientific-practical conference Marine and Coastal
Researches – 2013, Klaipėda, Lithuania, April 2013;
Scientific-practical conference Sea Science and Technologies –
2014, Klaipėda, Lithuania, April 2014.
The material of this study had been presented in two original
publications, published in peer-reviewed (ISI WOS) scientific
journals:
Gerok D., Bitinas A., 2013. Geophysical study of palaeo-incisions
in the Šventoji–Būtingė coastal area, north-west Lithuania. Baltica, 26
(2), 201—210.
8
Gerok D., Gelumbauskaitė L. Ž., Flodén T., Grigelis A., Bitinas
A., 2014. New data on the palaeo-incisions network of the
southeastern Baltic Sea. Baltica, 27 (1), 1–14.
Thesis structure. The dissertation includes ten chapters:
introduction, review of previous investigations, material and methods,
results, discussion, conclusions, references and three appendixes. The
material is presented on 114 pages, 39 figures, 11 tables and 3
appendixes. The dissertation refers to 102 literature sources. The
dissertation is written in English with an extended summary in
Lithuanian.
Acknowledgments. I would like to thank my supervisor Dr.
Albertas Bitinas for his support, patience and profound advices. I want
to express my deepest gratitude to Professor Algimantas Grigelis and
Dr. Živilė Gelumbauskaitė (Nature Research Centre, Institute of
Geology and Geography, Sector of Marine Geology and
Geodynamics) for having given me the possibility to use archive data
of the seismic graphic records collected during joined Lithuanian-
Swedish expeditions, consulting with methods and interpretation of
marine geophysical-geological data. I would like to thank Professor
Tom Flodèn (Stockholm University) for performed marine CSP data,
advice in their interpretation, comprehensive consulting and sharing
experience with me. Thanks to Professor Grigelis, Dr.
Gelumbauskaitė and Professor Flodèn for consulting with methods
and interpretation of marine geophysical-geological data. I would like
to thank Dr. Saulius Gulbinskas, Dr. Nerijus Blažauskas, Dr. Dainius
Michelevičius and Juozas Bičkunas for help in organization of the
land field investigations. My thanks to Jaunutis Bitinas and Viktoras
Lokutijevskis from Lithuanian Geological Survey for performed data;
Dr. Jonas Satkūnas for help during the seismic data digitizing; Dr.
Rimantas Šečkus for processing the data of electrical tomography; Dr.
Sergej Kanev for performed VSP data of several marine wells; Nikita
Dobrotin, Mindaugas Baliukonis and Manvydas Šaltis for help during
land field investigations; Mantas Budraitis and Dr. Dainius
9
Michelevičius for advice in applying the modern software. Thanks to
Dr. Nerijus Blažauskas and Dr. Rimantas Šečkus for reviewing the
final version of this work. I would like to thank Aloyzas Alius for
English grammar revising.
The on land geophysical acquisition described in this work has
been performed as a part of the Klaipėda University project
Technology and Environment Research Development of the
Lithuanian Maritime Sector (No VP1-3.1-ŠMM-08-K-01-019).
A b b r e v i a t i o n s .
Abbreviation Explanation 2D Two-dimensional
CDP Common depth point
CMP Common mid-point
CSP Continuous seismic profiling
GPR Ground penetrating radar
GPS Global Positioning System
LGS Lithuanian Geological Survey
MIS Marine isotope stage
RMS Root-mean-square
VSP Vertical seismic profiling
10
2. REVIEW OF PREVIOUS INVESTIGATIONS
2.1 GEOLOGICAL AND TECTONIC SETTINGS
2.1.1 Tectonic settings
The investigated area is located within the Baltic Syneclise which
is a regional depression in the western part of the East European
platform. In general, the axial part of the Baltic Syneclise extends in
NE–SW direction (Puura et al. 1991a). Folded structures and faults
with displacement amplitudes up to 170 m were formed in
westernmost Lithuania during the Early Ediacaran (Šliaupa, Hoth
2011). The tectonic activity had decreased and the marine
transgression had begun during the Late Ediacaran–Cambrian. Then
small-scale and sporadically distributed uplifts of the basement were
detected in the western Lithuania.
The main stage in the evolution of the Baltic Syneclise took place
in the Late Caledonian. Up to four kilometers of deposits had been
laid down in the axial part of the Baltic Syneclise at this time.
Intensive structural displacement of basement blocks took place in the
Carboniferous–Early Permian when the region was subjected to NE–
SW horizontal compression. As a result Polish–Lithuanian Syneclise
stretching to Tornquist–Teisseyre lineament was formed in the
Southern Baltic (Fig. 1; Grigelis 2011). E–W and NE–SW faults
dominates here, their amplitudes are from 50 to 200 m, and they dip to
the west at angles of 70–80o (in the Telšiai zone) (Šliaupa, Hoth
2011).
The Late Hercynian complex overlays azimuthally the irregular
Caledonian surface, often with an angular unconformity (Puura et al.
1991a). The complex consists of two structural levels, namely Early
Devonian–Carboniferous and Permian. Tectonic processes were
reactivated during the Late Devonian–Permian period. The maximum
thickness of the Hercynian complex (up to 1000 m) is located in the
Baltic Syneclise (Stirpeika 1999). From a tectonic point of view, most
11
structures, both the local and the major ones, were finally formed in
the Hercynian orogenesis (Suveizdis 1994b).
Fig. 1 The tectonic setting of the Baltic region after P. Suveizdis, 2003
(Grigelis, 2011).
The tectonic processes ceased in the Permian and restarted in the
Late Cretaceous. Inverse tectonic structures with amplitudes up to 200
m are identified in southern Lithuania and in the Kaliningrad Region
of Russia (Šliaupa, Hoth 2011). Modern tectonic processes are mostly
connected to postglacial relaxation (Puura et al. 1991a; Šliaupa 1981).
2.1.2 Stratigraphy
The investigated area is located in the central part of the Baltic
Syneclise of the East European platform, which was consolidated
during the Early Proterozoic (Šliaupa, Hoth 2011).
Achaean–Early Proterozoic (AR–PR1) crystalline basement is
located at a depth of c. 2 km in the area of investigation. It consists of
gneiss, biotitic granite–gneiss, crystallized shale, amphibolite,
quartzite, marble and volcanic rocks (Puura et al. 1991b).
12
After a break in sedimentation, the deposition was re-established in
the Ediacaran (Vendian). The deposits consist of siltstone,
sandstone, clay and conglomerate. The total thickness reaches 200 m
(Grigelis 1994a).
The Cambrian (Cm) is associated with marine terrigenous rocks:
sandstone, siltstone, argillite, clay and gritstone. The maximum
thickness ranges from 175 m on land in the western Lithuania to 288
m in the western Latvia. Offshore, the thickness ranges from 176 m in
the well D5 (Fig. 2, Appendix 1) to 213 m in the well E7 and 193 m in
the well D6 (Aliavdin et al. 1991; Appendix 1).
Fig. 2 Bedrock geology of the southeastern Baltic Sea (after Grigelis 2009,
modified 2012): 1 – area of investigation; 2 – wells (see Appendix 1); 3 –
faults.
Ordovician (O) sedimentary rocks overlay the Cambrian with
stratigraphic unconformity. The Ordovician deposits consist of
13
limestone, marlstone and clay. The deposits are between 60–160 m
thick in the offshore area and up to 210 m on land (Šliaupa, Hoth
2011). The top of Ordovician is a regional seismic marker.
The sedimentation significantly increased during the Silurian (S).
It is composed of argillite, dolomite, gypsum, limestone, carbonate
clay and is extremely rich in different fauna. The maximum thickness
is from 600 m in the well E7 to 870 m in the well D6 and up to 1000
m in the western Lithuania (Grigelis et al. 1991a).
Early Devonian (D1) deposits are composed of terrigenous rocks
(sandstone, siltstone and argillite) with intercalations of dolomite. The
thickness is about 150 m in the western Latvia and increases to the
south reaching c. 300 m (Grigelis et al. 1991b). A sedimentary break
occurs at the boundary between the Early and the Middle Devonian.
The Middle Devonian (D2) is represented by clayey–sandy and
sandy sediments, dolomite, marlstone and dolomitic breccia. The
maximum thickness varies from 200 m in the well D6 to 270 m in the
western Lithuania (Narbutas 1994).
Late Devonian (D3) deposits are composed of dolomite,
sandstone, siltstone and clay. The maximum thickness is presented in
the vicinity of Klaipėda, where it reaches up to 250 m (Narbutas
1994). The total thickness of the Devonian rocks ranges from 960 m
offshore Latvia to 1100 m near Klaipėda.
Carboniferous (C) rocks are of limited extent. They are developed
on land in Latvia and north-western Lithuania, but are absent in the
offshore part of the investigated area. They are represented by
sandstone and limestone with a thickness of up to 110 m (Šliaupa,
Hoth 2011).
Early Permian (P1) rocks are associated with gritstone and
sandstone, about 30 m thick, on land in Lithuania (Grigelis 1994a).
Late Permian (P2) rocks were deposited after a break in
sedimentation. They are absent in the western and northern parts of
the investigated area. They are composed of limestone, gypsum,
anhydrite and salt (in the southernmost part of the investigated area).
The thickness is 107 m in the well D6 and up to 150 m on land
(Suveizdis 1994a).
14
Early Triassic (T1) rocks are presented across almost the same
area as the Late Permian. They are composed of clay, siltstone and
sandstone, about 280 m thick in the well D6 and up to 200 m in the
western Lithuania (Suveizdis 1994c).
Middle Triassic (T2) – Early Jurassic (J1) rocks are absent in the
investigated area.
Middle Jurassic (J2) rocks and sediments overlay the Upper
Devonian, Permian and Triassic with a stratigraphic unconformity.
They are absent in the northwestern part of the investigated area.
Bathonian strata are composed of sandstone and clay. Their
maximum thickness reaches 50 m. Callovian strata are represented by
sand, sandstone, limestone and clay, also about 50 m thick (Grigelis et
al. 1991c; Grigelis 1994b).
Late Jurassic (J3) rocks and sediments are presented in western
Lithuania and in the southern offshore part of Lithuania. Marlstone,
clay, siltstone and sometimes limestone of Oxfordian age with a
maximum thickness of up to 85 m compose the Upper Jurassic in the
investigated area (Grigelis et al. 1991c).
Late Jurassic (J3) Kimmeridgian – Early Cretaceous (K1) strata
up to the Early Albian are absent in the investigated area.
Early Cretaceous (K1), Albian, rocks and sediments are
developed in the southern–southeastern part of the investigated area.
They are represented by sand and siltstone with intercalations of clay
and phosphorite concretions. The maximum thickness ranges from 28
m in the offshore area to 100 m on land (Grigelis 1994c).
Late Cretaceous (K2), Cenomanian–Santonian rocks and
sediments are distributed only in the southeastern part of the
investigated area. They are composed of sand, sandstone, siltstone,
limestone and marlstone. They are about 100-m thick in the offshore
area and up to 200 m on land in the western Lithuania (Grigelis
1994b).
Quaternary (Q) deposits cover the entire area of investigations.
They are described in detail below (see Chapter 2.1.5).
15
2.1.3 The seismostratigraphic framework
T a b l e 1 . S t r a t i g r a p h i c s u b d i v i s i o n a n d
b o u n d a r i e s o f t h e L a t e P a l e o z o i c a n d M e s o z o i c
s t r a t a i n t h e s o u t h e a s t e r n B a l t i c S e a ( F l o d è n
1 9 8 0 , G r i g e l i s 1 9 9 9 ) .
STRATIGRAPHY Environment
Seismic
unit Period Epoch Age Formation
Cretaceous
Late
Santonian,
Coniacian,
Turonian
Brasta
Formation Marine K2
Cenomanian Labguva
Formation Shallow
marine K1
Early Albian Jiesia
Formation
Jurassic
Late Oxfordian Ažuolija
Formation Marine J4
Middle
Callovian
Skinija
Formation
Paprtinė
Formation
Shallow
marine
J3
J2
Bathonian
Skalviai
Group
(upper part)
Brackish
water basin J1
Triassic Early Purmaliai
Group
Continental
basin
T2
T1
Permian Late Zeichstein
Werra Cycle
Naujoji
Akmenė
Formation Shallow
marine
P2 – P3
Sasnava
Formation P1
Kalvarija
Formation
Devonian Late
Frasnian
Gauja Beds
to Amula
Beds
Shallow
marine
D3 –
D4
16
The lithology and internal structure of geological layers are the
basics of the seismostratigraphic subdivision. Seismic boundaries are
the reflections of the boundaries between geological units. In addition,
seismic reflectivity patterns respond to the structure of geological
layers. This fact may be also used to locate the boundary between
different geological layers. Especially in the cases, when the reflection
of the boundary is indistinct and weak.
The exposed sedimentary bedrock of the investigated area ranges
from Middle Devonian to Late Cretaceous (Table 1; Fig. 2).
Four seismically contrastive units can be identified into the
Devonian sedimentary sequence, but only one of these units with
mainly marine deposits is presented in the investigated area. The
stratigraphic subdivision is based on lithological and biostratigraphical
evidence from offshore Latvia. Seismic unit D3–D4 is subdivided and
interpreted as D3 Frasnian rocks. The Baltic Sea transgressed in the
Frasnian age. Clay, marl, limestone and dolomite were deposited
(except for short intermissions) in the sea at that time. The D3–D4
unit may be further subdivided into two seismic intervals: a lower
interval is characterized by particularly weak seismic reflectivity
pattern and an upper one by a more distinct seismic pattern (Fig. 3).
Both intervals display irregular bedding with frequent sedimentary
breaks. A rather strong and stable reflector separates these two
intervals. This reflector forms an important seismic marker within the
unit and is traceable across a large area. The maximum thickness of
the D3–D4 unit is about 200 m in rather equal proportions between the
intervals (Flodén 1980).
A distinctly layered seismic reflectivity pattern is a characteristic
for the Late Permian offshore (Fig. 4). It is interpreted as the lower
part of the Zeichstein Werra cycle with typical seismic signatures
(from bottom to top): P1 unit consists of dolomite or limestone; P2
unit – hard limestone and dolomite with concretions of silica; P3 unit
– carbonate strata. The P2 unit is affected by palaeokarsts and
becomes thicker in the direction of the Lithuanian shoreline (Grigelis
17
1999). The maximum observed thickness of the Late Permian within
investigated area is 107 m in the well D6 (Appendix 1).
Fig. 3 Example of seismic unit D3–D4 from the area SE of Gotland. D3 —
base Gauj (base of Upper Devonian), D4 — base Mur (base of Upper
terrigenous Devonian) (after Flodén 1980).
Fig. 4 Examples of seismic units P2, P3 and T1 from the SE Baltic Sea (after
Grigelis 1999).
18
The seismic reflection of the Early Triassic is facially separated
into two units: T1 and T2. Both units are interpreted as Early Triassic
argillite, supposedly equivalent to the Purmaliai Group. T1 seismic
unit is expressed by a comparatively weak regular seismic reflectivity
pattern (Fig. 4). It is presented in the southeastern part of the
investigated area. The T1 unit is regarded as lowermost part of the
Nemunas Formation. T2 seismic unit is interpreted as equivalent to
the Early Triassic Palanga Formation. This unit is characterized by a
comparatively weak, irregular and typically transparent seismic
reflectivity pattern (Fig. 5). The irregularities of the seismic
reflectivity pattern are most evident in the northern part of the
investigated area. The maximum thickness of the Early Triassic is
about 50 m (Grigelis 1999).
Fig. 5 Examples of seismic units T2, J1 and J2 from the SE Baltic Sea (after
Grigelis 1999).
The seismic reflection of the Middle–Late Jurassic is subdivided
into four seismically derived units. J1 unit is associated with
terrigenous brackish water deposits equivalent to the upper part of the
Middle Jurassic Skalviai Group. It is characterized by an almost
transparent seismic reflectivity pattern (Fig. 5; Fig. 6). The maximum
thickness is 25 m. J2 unit is associated with Early Callovian sandy
19
carbonate deposits and is referred to the Papartinė Formation. It is
characterized by a horizontally layered seismic reflectivity pattern
with several strong internal reflectors (Fig. 5; Fig. 6). The J2 unit is
conformed to the maximum northwestern transgression. The
maximum thickness of this seismic unit is 50 m. J3 unit is regarded to
represent the Skinija Formation of Late Callovian age. It is composed
of argillaceous clay and silt. The seismic reflectivity pattern is similar
to the J2 unit, but separated from it by a distinct reflector in the
eastern part of the offshore area (Fig. 6). The maximum thickness
reaches 70 m. J4 unit is referred to the Oxfordian argillaceous
carbonate deposits equivalent to the Ąžuolija Formation. It is
expressed by a distinct layered seismic reflectivity pattern and is
distributed in the southern part of the investigated area. The maximum
thickness of this unit is up to 75 m.
Fig. 6 Examples of seismic units J1, J2 and J3 from the SE Baltic Sea (after
Grigelis 1999).
The seismic reflection of the Cretaceous is subdivided into two
seismically contrastive units. K1 unit is characterized by terrigenous
quartz–glauconitic deposits of Albian and Cenomanian and regarded
to the Jiesia and Labguva Formations. K1 unit may be subdivided into
two seismic intervals: a lower interval with a weakly layered seismic
reflectivity pattern and an upper interval with a regularly layered
20
seismic pattern. The maximum thickness is about 80 m. K2 unit is
interpreted as Turonian–Santonian carbonate chalky deposits of the
Brasta Formation. It is described by a distinct coherent seismic
reflectivity pattern. The maximum thickness of this seismic unit is
about 100 m (Grigelis 1999).
2.1.4 The sub–Quaternary surface
The first version of the sub–Quaternary surface map of the south-
eastern Baltic Sea with palaeo-incisions was compiled and described
in 1995 (Gelumbauskaitė 1996). Later this scheme was updated
having applied new data. The topography of the sub–Quaternary
morphostructure is characterized by uplifts, depressions and structural
terraces (Gelumbauskaitė, Litvin 1986; Gelumbauskaitė 1996;
Gelumbauskaitė, Grigelis 1997) (Fig. 7).
The recent sub-Quaternary relief of the southeastern Baltic region
was formed during Late Paleogene–Neogene regression and
peneplenization. Erosion and denudation processes were active due to
uplifting of the area in the end of the Neogene (Gelumbauskaitė
1999).
Late Devonian Klaipėda–Liepaja Uplift namely the structural
terraces of the banks (Fig. 7), was formed in the Pļaviņas–Pamūšis
time. The Uplift separates the East Gotland Trough from the Gdansk
Depression. Its top occurs at an absolute depth from –40 to –60 m.
The Curonian Plateau and the Gdansk Depression are located on the
peneplain formed in the Late Permian–Cretaceous rocks.
The palaeo-incisions of the Eastern Trough of the Gotland
Depression, cut into the structural–denudational surface of the
Middle–Late Devonian rocks, were examined in seventy three
segments. The absolute depth of these incisions ranges from –207 to –
337 m (Gelumbauskaitė, Grigelis 1997).
21
Fig. 7 The sub–Quaternary surface of the southeastern Baltic Sea (after
Gelumbauskaitė 1995). Subdivision of morphostructure: I – Eastern Gotland
Through; II – Klaipėda-Liepaja Uplift; III – Gdansk Depression; IV –
Curonian structural terrace. Segments of the palaeo-incisions are in absolute
depth in meters.
22
Land part of sub–Quaternary surface is formed during the
Oligocene/Neogene uplift and denudation. The map has been
compiled essentially having applied data from the regular geological
mapping supplemented by well data (Šliaupa et al. 1994).
The most recent land geological mapping has been performed by
the Lithuanian Geological Survey from the Lithuanian coastline and
eastwards to 22o E.
2.1.5 Thickness of Quaternary cover
Quaternary cover in the south–eastern Baltic Sea was evaluated by
Gelumbauskaitė in 1996. In general, the Quaternary thickness varies
from 5 m to 20–25 m on the plateau and reaches 40 m in the
depressions. Shoreward in the coastal zone, the thickness of the
Quaternary cover increases up to 50–60 m. The lithostratigraphy is
based on short drill core data analysis. These cores are drilled through
the entire Quaternary depositional complex (data from the marine
geological mapping at the scale of 1:500 000/1:200 000 in 1975–1978;
engineering geological research of PETROBALTIC in 1989–1990).
The depositional Pleistocene–Holocene complex varies from 10 m in
the shallow zone to 48 m on the Klaipėda Slope (on E–W Klaipėda
traverse) (Majore et al. 1997; Gelumbauskaitė 2009).
According to continuous seismic profiling data, three separate till
units, clay, and also stratified and unstratified layers of sand and
gravel, have been established in the Baltic Proper. It is possible to
classify at least three generations of palaeo-incisions (Table 2). These
three generations of palaeo-incisions are associated with Elsterian,
Saalian, and Weichselian glaciations respectively (Bjerkéus et al.
1994). The palaeo-incisions are infilled by till and stratified, or
unstratified, glaciofluvial material, and all the palaeo-incisions are
covered by sediments of the Weichselian glaciation. Weichselian till is
developed in a significant part of the Baltic Sea bottom except
particular near shore areas, where it was eroded during different stages
of the Baltic Sea formation in Holocene, and where Saalian till
outcrop on the seafloor (Repečka et al. 1991; Bitinas et al. 1999).
23
T a b l e 2 . C h r o n o s t r a t i g r a p h i c s u b d i v i s i o n o f t h e
P l e i s t o c e n e d e p o s i t s i n t h e L i t h u a n i a n c o a s t a l
z o n e a n d t h e i r l i t h o l o g i c a l c h a r a c t e r i s t i c s * .
Chrono-
stratigra-
phic stages
Marine
isotope
stage
Time
scale,
ka BP
Genesis and lithology of sediments
Holocene 1 11.6
Marine, lagoon, lacustrine, aeolian,
alluvial deposits and sediments: sand,
mud, gyttja, peat, silt.
Weichselian
2
24
Glacial deposits. Upper till: yellowish
brown, soft and slightly weathered.
Lower till: brownish grey and greyly
brown, contains glacio-dislocated
floes of glaciofluvial gravel, sand.
3 59 Lacustrine sediments: greyish-yellow
or greyish-brown fine-grained sand.
4
74
Glacial deposits: till, grey and
greenish-grey, in some places grey-
brown, compact. In the environs of
the Klaipeda Strait contains a big
amount of glacio-dislocated floes of
lacustrine sediments with organic.
5a-d 117 Lacustrine sediments: greyish-yellow
fine- and very fine-grained sand.
Saalian
complex
6-10
337
Glacial lacustrine sediments: greyish-
yellow fine- and very fine-grained
sand or silty sand with admixture of
finely dispersive organic matter; in
some places with interlayers of gyttja
or peat. Glacial deposits: compact
greyish-brown or grey till.
Elsterian
12
478
Glacial deposits: compact grey and
greenish-grey till developed in the
depressions of sub-Quaternary relief
and palaeo–incisions.
24
*Chronostratigraphic units and time scale – after Gibbard, Cohen
2008; Guobytė, Satkūnas 2011. Stratigraphic subdivision and
lithology – after Bitinas et al. 1999, 2000, 2004, 2011;
Molodkov et al. 2010; Damušytė et al. 2011.
Quaternary thickness varies in relatively wide range from 20 m in
the southern part of investigated area up to 60–80 m in the northern
part. It reaches up to 130–140 m in the palaeo-incisions. Tills prevail
in the upper and in lowermost parts of the Quaternary strata. An inter-
till complex of sediments is developed in the middle part. Three till
layers are established in the lowermost part of the Quaternary strata.
They most probably represent Elsterian and Salian glacial sediments
(Table 2). A more detailed stratigraphic identification of the oldest
Pleistocene tills is complicated, because no section with interglacial
sediments, i.e. marine sediments of Holsteinian and Eemian Seas, has
been found on the Lithuanian Baltic coast or offshore. According to
the results of luminescence dating, the inter–till complex of sediments
was formed in a few sedimentary basins during late marine isotope
stage (MIS) 6, MIS 5d-5a, and MIS 3 (Molodkov et al. 2010; Bitinas
et al. 2011). Till layers from the uppermost part of geological section
represent a few glacial advances of the Weichselian glaciation
(occurred during MIS 4 and MIS 2) (Bitinas et al. 2011). MIS 4 and
MIS 2 strata include a large amount of Pleistocene floes. Both this fact
and glaciotectonic deformations are key features of MIS 4 and MIS 2
Weichselian glacial stages.
2.1.6 Geological features of palaeo-incisions
The distribution of palaeo-incisions is irregular and complicated
(Sviridov 1984). Thus, the present day published schemes (Gaigalas
1976; Šliaupa, Repečka 1995; Šliaupa 2001) and maps of sub-
Quaternary surfaces (Sviridov et al. 1976; Šliaupa et al. 1994; Šliaupa
2004) on land in the western Lithuania with evidences of palaeo-
incisions are not detailed enough to serve as guidelines for
investigating palaeo-incisions.
25
In general, palaeo-incisions appear as buried valleys, most often
filled with Quaternary sandy-clayey deposits in various combinations.
The shape of these geological structures looks slightly similar to river
valleys. Commonly these structures are of U- or V-shape in
perpendicular profile, with the angle of slopes reaching 40o–45
o. The
width of palaeo-incisions varies from a few meters (Piotrowski 1994)
to several hundred meters and even up to 5 km according to some
estimation (Šliaupa 2004; Smit, Bregman 2012; Atkinson et al. 2013).
The depth of palaeo-incisions varies from several meters to 300 m.
Depth of 300 m in absolute values is reported from the Dutch sector of
the North Sea. The width of the structures exceed the depth by about
10 times (Huuse, Lykke–Andersen 2000; Smit, Bregman 2012). The
length of palaeo-incisions may reach 100 km (Janszen et al. 2012).
Palaeo-incisions are mainly filled in with Pleistocene sediments to
their average depth of 80 m. Several different infilling units, i. e. tills,
clay, sand and gravel deposits have been classified in the southeastern
Baltic Sea in the eastern part of the Baltic Proper (Bjerkéus et al.
1994; Flodén et al. 1997). The infilling of the palaeo-incisions often
indicates two, or sometimes three, depositional events.
The prevailing relative depth of the palaeo-incisions is about 40–70
m in the Lithuanian coastal area; merely a few of them are deeper as
e.g. a palaeo-incision reaching an altitude of –147 m in the vicinity of
Šventoji. The deepest palaeo-incision in this area has been recorded in
a borehole drilled in the Nemunas Delta area; its bottom reached an
altitude of –269 m (Šliaupa 2004).
Different opinions have been put forward with regard to the
genesis of palaeo-incisions in the sub-Quaternary surface. Numerous
studies favor an idea of a complex stepwise periglacial, sub-glacial-
glaciofluvial, postglacial-fluvial origin of the palaeo-incisions that
were then even further reshaped by the next generation of Pleistocene
glaciers (Timofeev et al. 1974; Gaigalas 1976; Sviridov et al. 1976;
Gudelis et al. 1977; Blazhchishin et al. 1982; Tavast, Raukas 1982;
Eberhards, Miidel 1984; Sviridov 1984; Veinberga et al. 1986;
Rozhdestvensky 1989; Repečka et al. 1991; A. Šliaupa et al. 1995;
Savvaitov et al. 1999). Initially it had been noted that the zones with
26
fragments of incisions extended clearly in the NE–SW direction,
responding to the distribution of the soft sedimentary rocks of the
Triassic, Jurassic and Cretaceous geological systems, respectively
(Sviridov 1984, 1991). Later on, an idea was expressed on possible
links between glacial-sub-glacial incisions and fossil cryogenic
structures in the Mesozoic bedrock of the southeastern Baltic Sea
(Monkevičius 1999).
Other authors have put forward a sub-glacial or more precisely a
sub-glacial–fluvioglacial hypothesis. It is based on that the palaeo-
incisions are the result of glacier-derived water erosion caused by
catastrophic releases of huge water masses under the high pressure
during ice recession (Kuster, Meyer 1979; Ehlers et al. 1984;
Wingfield 1989; Bjerkeus et al. 1994; Flodén et al. 1997; Bitinas
1999; Jurgens 1999; Satkūnas 2000, 2008). This hypothesis is based
on the theory of melt-water circulation under continental ice sheet
(Boulton, Hidmarsh 1987; Boulton et al. 1993; Piotrowski 1994,
1997; Boulton, Caban 1995; Boulton et al. 1995). J. Satkūnas (2000)
particularly analyzed palaeo-incisions in Lithuania and deduced that
lowering of the global ocean-level is not sufficient to explain the
intensive entrenching of palaeo-rivers and formation of palaeo-
incisions. The palaeo-incisions of some generations had been
determined to repeat each other in the same places. This fact is also
confirmed by the results of marine seismic profiling in the Baltic Sea
(Sviridov 1984; Bjerkeus et al. 1994) and in the North Sea (Wingfield
1989).
Used marine data, which originate from seismo-acoustic
investigations in the southeastern segment of the Central Baltic Sea,
show that the palaeo-incisions are imprinted into the Neogene
peneplain surface here. They are weakly expressed as compared to the
palaeo-incisions in the subsurface of the Middle Devonian terrigenous
rocks along the eastern slope of the Gotland depression (Bjerkéus et
al. 1994; Gelumbauskaitė, 1996; Flodén et al. 1997). Their connection
to the fragmented system of late- to post-glacial channels in the Late
Quaternary sequence of the study area is not clear yet. Otherwise,
geophysical surveys in the central western part of the Baltic Sea, e.g.
27
in the Hanö Bay, have not revealed any similar structures which
strongly indicate that the valleys are truly of a general periglacial
origin generated during major standstills of ice sheets (Flodén et al.
1997).
Some scientists do not associate palaeo-incision infill with any
specific glaciation (Janszen et al. 2013). It corresponds with the fact,
that various seismic reflectivity patterns of tills confirm the complex
and differential infill of palaeo-incisions. Geophysical methods, which
have been used during this study, are suitable only for detection of
location, morphology and infill of palaeo-incisions, but they do not
allow establishing their genesis or accurate age.
2.2 OVERVIEW OF PREVIOUS GEOPHYSICAL
ACTIVITY
2.2.1 Marine continuous seismic reflection profiling (CSP)
In the 1970s, the pioneers of shallow seismo-acoustic surveys of
the Baltic Proper were investigators of the Stockholm University
dealing with the distribution of Paleozoic sedimentary rocks, as well
as the researchers from the Atlantic Branch of Kaliningrad
Oceanology Institute working in the area where Mesozoic and
Cenozoic rocks are abundant. At this time the methods and equipment
of continuous seismic profiling (CSP), focused on the upper parts of
the pre–Quaternary rocks (0–200 m), were successively developed
improving the quality of the seismic records. The research area was
covered by a dense network of seismo-acoustic profiles surveying the
sub–Quaternary surface relief, structure of the Mesozoic and Cenozoic
sedimentary cover, displacements in the upper part of sedimentary
cover in the south–eastern Baltic Sea (Sviridov 1976, 1983). At the
same time, the geology, tectonics and seismostratigraphy of the
Paleozoic bedrock of the Central Baltic had been studied in detail
(Flodén 1980). In 1984, the data of the Mesozoic and Cenozoic
sedimentary rocks in the south–eastern part of the Central Baltic Sea
had been summarized displaying different surface heterogeneities, in
28
particular including local palaeo-incisions (Fig. 8; Sviridov 1984,
1991). For the first time it was noted that distinguished zones of
fragmentation extend in the NE–SW direction and correspond to the
distribution of the soft sedimentary rocks of the Triassic, Jurassic and
Cretaceous geological systems, respectively. Later on, an idea was
expressed on possible links of glacial–sub-glacial incisions with fossil
cryogenic structures in the Mesozoic bedrock of the southeastern
Baltic Sea (Monkevičius 1999).
Fig. 8 The distribution of surface heterogeneities in the southeastern Baltic
region by continuous seismic profiling and land data. 1 – Local palaeo-
incisions: a – without reflection boundaries, b – with reflection boundaries; 2
– zones of fragmentation; 3 – glacial and fluvial palaeo-incisions on land
(after Sviridov 1984).
29
General geological schemes of the pre–Quaternary sedimentary
rocks of the Central Baltic Sea had been set in the mid-1960s tracing
the boundaries of the geological systems seawards from the East
Baltic mainland and from Scandinavia (Gudelis 1970).
Later on, in the last decades of the 20th century, the knowledge of
the bedrock geology of the Baltic Proper increased significantly
through deep seismic surveys, hydrocarbon prospective drillings and
tectonic analyses ranging over an internal structure of entrails. Studies
of marine drilling cores applying mainly micropalaeontological
methods allowed the exploration of the pre-Quaternary stratigraphic
section in the eastern segment of the Baltic Proper (Grigelis 1995).
Moreover, continuous seismic profiling (CSP) data, shot during
Lithuanian-Swedish marine geological–geophysical expeditions in
1993–1995 (Grigelis et al. 1994, 1996), provided a reliable source for
detailed investigations of the upper parts of the sub–Quaternary
bedrock of the Central Baltic Sea (Fig. 9; Grigelis 1999). An idea was
developed about the presence of sub–Permian and sub–Quaternary
peneplains in the southeastern Baltic Sea. This facilitated the
construction of a modern geological map (Grigelis 1995). The next
step was to establish the seismo–stratigraphic units and boundaries of
the Late Paleozoic (Permian) and Mesozoic bedrock of the
southeastern segment of the Baltic Sea (Grigelis 1999). That
supplemented the seismo–stratigraphy of the Paleozoic of the Central
Baltic Sea defined in the late 1970s (Flodén 1980).
Several geological maps of the Central Baltic Sea, and of the entire
Baltic Sea, have been compiled since 1980 based on more or less
relevant geological–geophysical data (see Grigelis et al. 1993;
Grigelis 2011). A basic geological map of the Central Baltic Sea, the
original version at a scale of 1:500 000, had been compiled by A.
Grigelis in 1998 (see Fig. 1). Later this map was integrated into the
geological map of Northern Europe (Sigmond, Ed. 2002) and in the
International geological map of Europe (IGME–5000; Asch, 2005).
The most recent version is used in the digital release of the One
Geology Europe elaborated in 2011–2012 (Stevenson 2012).
30
Fig. 9 Location of seismic lines in the southeastern part of the Baltic Sea.
Expeditions: 1 – Grigelis et al. 1994; 2 – Grigelis et al. 1996 (1994
expedition); 3 – Grigelis et al. 1996 (1995 expedition).
2.2.2 2D seismic common mid-point (CMP) shooting on land
The western part of Lithuania is covered by a rather dense grid of
seismic lines, shot by the common mid-point technique. The objective
of these investigations had been Cambrian–Silurian oil and gas
perspective sedimentary rocks (Zdanavičiūtė, Sakalauskas 2001). The
uppermost part of the sedimentary cover, down to a depth of c. 150 m
had not been resolved during these investigations. But in the context
of this work that is an area of primary interest.
The geological section of well No. 19623 is used as a key-section
for choosing theoretical physical properties of the sedimentary rocks
(Table 3).
31
T a b l e 3 . R e l a t i v e p e r m i t t i v i t y ( ε ) a n d s e i s m i c
v e l o c i t y o f p - w a v e s ( m / s ) i n w e l l 1 9 6 2 3 * .
To
p o
f t
he
lay
er
Bo
tto
m o
f
the
lay
er
Ag
e
Ro
ck
Rel
ati
ve
per
mit
tiv
ity
(ε)
3S
eism
ic
vel
oci
ty
(m/s
)
4R
esis
tiv
ity
r, Ω
. m
0 0.5
Q
Peat 111
≤ 1800 30 –
100
0.5 4 Sand 24 – 9
4 8 Peat 111
8 11 Sand 24 – 9
11 16 Till 29 – 25
16 21 Gravel with
sand 24–9
21 83 Sand 24–9
83 95 Gravel with
sand
95 104 Till
104 124 Sandy till
124 129 Gravel with
sand
129 135 Till
surrounding
bedrock
T1 Clay 2100 –
2300 4 – 15
135 162 P2 Limestone 2000 –
3000
90 –
5000
162 174 C1–
D3
Marlstone 2400 –
2500
174 190 Sandstone
190 210 Marlstone
210 240 D3 Dolomite 2450 –
2650
32
*(Lithuanian Geological Survey database,
http://www.lgt.lt/zemelap/main.php?sesName=lgt1412160593, for
location see Fig. 20B). 1 – After Ayalew et al. 2007;
2 – after Vladov,
Starovoytov 2004; 3 – Vertical Seismic Profiling (VSP) data from well
D5; 4 – after Šečkus 2002.
2.2.3 Electrical tomography
The electrical tomography is used during geological, hydrological,
ecological and engineering investigations in Lithuania. The object of
these investigations is the uppermost part of the sedimentary cover,
down to a depth of c. 200 m. It corresponds to an area of primary
interest in the context of this work. The electrical tomography is the
most commonly used geophysical method for electrical surveys in
Lithuania (for example, see Fig. 10, Šečkus 2002).
Fig. 10 Line Kleboniškis-1. Inverse model resistivity section (after Šečkus
2002).
The applying of electrical tomography method is described below
(see Chapter 3.2.2).
2.2.4 Gravimetric survey
A test gravimetric survey had been performed in the Dovilai area
(Klaipėda District) by L. Korabliova in 1996–2000. This survey is part
of the integrated geological mapping at the scale of 1:50 000 carried
out by the Lithuanian Geological Survey. The objective of the
investigation had been the testing of application of gravimetric
methods for identification of palaeo-incisions in the particular
33
geological settings that exist in this part of the Lithuanian coastal area.
Thus, a palaeo-incision is contoured along the one gravimetric profile
in the Dovilai area and confirmed by the section in the well Dovilai-11
(Fig. 11). The geophysical model of the Quaternary thickness and the
uppermost part of the pre-Quaternary sedimentary bedrock had been
carried out by L. Korabliova (Bitinas 2000). The geological section
along the above gravimetric profile and via well Dovilai-11 has been
compiled, based on these data.
Fig. 11 Results of the gravimetric survey. A: Measured values (dots) and the
Bouguer gravity anomaly (polyline). B: The geophysical model; ρ – density.
C: Geological interpretation, gQII – glacial deposits of the Middle
Pleistocene; agQIII – aqua-glacial deposits of the Last Glaciation inside the
palaeo-incisions. Geophysical measurements and model after L. Korabliova.
Based on the results of the gravimetric survey, the following
conclusions have been made:
34
(1) It is possible to locate a palaeo-incision applying gravimetric
measurements alone, but there are gravitational anomalies in the area,
which are not connected to palaeo-incisions (e.g. at the position 1700
– 2200 m in Fig. 11B). It is impossible to determine the origin of a
gravitational anomaly without additional geological or geophysical
data. Thus, the location of palaeo-incisions is not fully verified
applying the gravimetric survey method alone.
(2) It is almost impossible to determine the depth and locate the
slopes of the palaeo-incisions. Nor it is possible to separate the
geological layers of enclosing rocks without additional geological or
geophysical data.
3. MATERIAL AND METHODS
The Palanga–Šventoji area along the Lithuanian coast has been
chosen as a key-area for the detailed experimental investigations (Fig.
12). This area is selected because it contains a number of boreholes,
which aided in locating the palaeo-incisions (Bitinas et al. 1998). 2D
shallow seismic and electrical tomography, has been applied to locate
palaeo-incisions on land in the western Lithuania (Table 4).
Fig. 12 Areas of investigation. 1 – Area of compiled set of the pre-
Quaternary maps; 2 – location of CSP data (see Fig. 14); 3 – the area of
geophysical investigations on land (see Fig. 20); 4 – Lithuanian Sea border.
35
This work also contains a detailed analysis of analogous single–
channel continuous seismic profiling data (CSP) in the southeastern
part of the Baltic Sea (Fig. 9). The investigated area offshore is
located within the Lithuanian economic zone and adjacent areas,
where the CSP data are available (Fig. 12). The data have been
collected by the Institute of Geology and Geography and also by the
Stockholm University.
T a b l e 4 . S c o p e o f g e o p h y s i c a l i n v e s t i g a t i o n s
Method Continuous
seismic profiling
2D CMP
seismic
Electrical
tomography
Location Offshore On land On land
Status Digitalized and
re-interpreted
Newly
investigated
Newly
investigated
Total length, km 2233.1 6.9 2.6
3.1 CONTINUOUS SEISMIC PROFILING (CSP) FOR
MARINE INVESTIGATIONS
The main principle of continuous seismic profiler (CSP) is that, the
signal penetrates into the sea floor, where it is reflected at velocity
discontinuities (seismic boundaries) in the sediment or bedrock (Fig.
13).
Fig. 13 The seismic profiler: 1—transmitter (seismic source); 2—hydrophone
(seismic receiver); 3 – theoretical trace of seismic reflected wave; 4 – seismic
boundaries; 5 – water layer; V1 and V2 – geological layers with different
seismic velocities.
36
The reflected signals are recorded by a single channel hydrophone,
which is constructed to have its maximum sensitivity perpendicular to
the survey line (Flodèn 1980).
The data used in this investigation had been collected during joint
geological–geophysical surveys performed by the Lithuanian Institute
of Geology and Geography (Department of Baltic Marine Geology)
and Stockholm University (Department of Geology and
Geochemistry) in 1993–1995 and in 1998–1999 (Grigelis et al. 1994,
1996; http://www.eu-seased.net: Seismic and sonar/Euroseismic/
metaformat) (Fig. 14; Appendix 2).
Fig. 14 Location map of CSP lines 2014: 1 – isobaths are drawn at 5 m
intervals; 2 – Lithuanian Sea border; 3 – fragments of seismic lines (see
Figs. 15 – 19, 30, 32 – 34); 4 – seismic lines interpreted and reinterpreted
during this work; 5 – earlier interpreted seismic lines used as basis for
general seismic data interpretation; 6 – wells (Appendix 1).
37
Seismic lines are located every 5 km in the eastern part and every
10 km in the western and northern parts of the investigated area. In the
central part of the area the lines are located every 2.5–5 km and a set
of NW–SE lines every 2 km. Total length of the 62 seismic lines
studied is 2233 km (Appendix 2, Table 4).
A PAR-600B air gun, 100–1000 Hz at 14 MPa, was used as seismic
source and a hydrophone eel of 20 m length as seismic recorder. The
record sweep was 0.5 s, which is sufficient to obtain seismic data
down to about 500 m depth (b. s. l.) in the area of investigations. The
signal processing was done on site, and both stacked and unstacked
records, band pass filtered 200–500 Hz, were displayed on precision
graphic recorders. An echo sounder, FURUNO FE-881 MK-II, was
used to record water depth. A Raytheon, and later a NavTrackXL, GPS
navigator was used for positioning. The obtained accuracy was ± 50
m. A graphical coordinate system based on the WGS-84 geoid was
chosen to fix the position of the seismic lines (see Appendix 2).
The seismic records were used to detect the offshore palaeo-
incisions and analyze and describe their infillings. Three offshore
wells – 54M, 58M and D11-1P (Fig. 14) – have been drilled into
palaeo-incisions. The deposits of the infillings have been analyzed and
a correlation between the seismic reflectivity pattern and the type of
infilling has been determined. Based on the comparison with the well
data, the seismic reflectivity pattern of about one hundred fragments
of seismic profiles crossing the palaeo-incisions were analyzed
(Appendix 3). The investigated area is 67 km from north to south and
82 km from west to east, 19.5 km2.
The general features for locating palaeo-incisions are as follows:
differences in internal seismic reflectors between the incision and the
surrounding bedrock, phase shift, and breaks of distinct seismic events
at the boundary of a palaeo-incision, as well as increased amplitudes
of the internal seismic reflectors within the incision (Table 5).
38
T a b l e 5 . C r i t e r i o n s f o r d e t e r m i n i n g s l o p e s o f
p a l a e o - i n c i s i o n s a c c o r d i n g t o c h a r a c t e r o f
s e i s m i c r e c o r d .
Type of
boundary Criterion Example
1 Differences in character of internal
seismic reflectors between the incision
and surrounding bedrock
2 Breaks of distinct seismic events at
boundary of palaeo-incisions
3 Phase shift of the same seismic
reflectors at boundary of palaeo-
incisions
4 Higher amplitudes of the internal
seismic reflectors within palaeo-
incisions
The interpretation of seismic lines 9302, 9404, 9405 and 9410
(Bjerkéus et al. 1994; Grigelis et al. 1994, 1996; Gelumbauskaitė
1995; Flodén et al. 1997; Gelumbauskaitė, Grigelis 1997;
Gelumbauskaitė 1999, 2000) has been digitalized. Together with well
39
data, it provided the basis for general seismic data interpretation
presented in this work (Fig. 15).
Fig. 15 A: Fragment of seismic line 9410B with interpretation; B: geological
section corresponding to A. 1 – seafloor; 2 – top of J4 seismic unit; 3 – top of
J2 seismic unit; 4 – inferred top of T1 seismic unit; 5 – multiple reflection
from the seafloor (location see Fig. 14).
All the analogous, paper-based seismic records were digitalized.
Each seismic record was of a rectangular form with a height of 1
40
meter and length from 5 to 50 meters. Digital visualization makes it
possible to change the scale and the gain of seismic records, to make
additional processing of the seismic data, and also to correlate the data
of different coordinate systems. Therefore the quality of seismic data
interpretation is more precise. Moreover, the time, needed for
interpretation and data copying, significantly decrease.
The seismic data have been reinterpreted applying the Halliburton
Geographix software (identification of geological boundaries was
done manually). First the analogous seismic recordings were digitized
with Mathworks Matlab, SegyMat (free open software) and
IMAGE2SEGY (Barcelona Institute of Marine Science) to Seg-Y file
format. Next, all the newly created seismic files were imported to the
Halliburton Geographix software format. Likewise it was made for
the first time (Grigelis 1999), seismic units (Table 1) were interpreted
having applied data from the offshore wells D5, D6, E6 and E7 (see
Figs. 16 – 19; Appendix 1). The tops of the seismic units J4, J2 and T1
were connected to the well D5 (Fig. 16), the top of units K1, J4, J2 –
to the well D6 (Fig. 17). The top of D4–D3 seismic unit was
connected to the wells E6 (Fig. 18) and E7 (Fig. 19).
Fig. 16 A: Fragment of seismic line 9404 with interpretation; B: geological
section corresponding to A. 1 – seafloor; 2 – top of J4 seismic unit; 3 – top of
J2 seismic unit; 4 – top of T1 seismic unit; 5 – multiple reflection from the
seafloor; 6 – well (location see Fig. 14).
41
Fig. 17 A: Fragment of seismic line 9302 with interpretation; B: geological
section corresponding to A. 1 – seafloor; 2 – top of K2 seismic unit; 3 – top
of J4 seismic unit; 4 – well (location see Fig. 14).
Fig. 18 A: Fragment of seismic line 980830_ with interpretation; B:
geological section corresponding to A. 1 – seafloor; 2 – top of D3-D4 seismic
unit; 3 – multiple reflection from the seafloor; 4 – well (location see Fig. 14).
42
Fig. 19 A: Fragment of seismic line 980901_3 with interpretation; B:
geological section corresponding to A. 1 – seafloor; 2 – top of D3-D4 seismic
unit; 3 – multiple reflection from the seafloor; 4 – well (location see Fig. 14).
The selection of seismic horizons and their correlation at the
intersections of the lines are realized in Halliburton Geographix
software in the time domain. The seismic boundaries of the bedrock
are generally rather distinct and are easily traced along the seismic
sections. In places of low reflectivity it is also possible to separate the
seismic units by geometric shape, amplitude and the configuration of
the seismic reflections. Correlation by time between seismic sections
was done having used the seafloor reflection as a seismic marker. The
maximum time shift between all the seismic sections is 8 ms.
3.2 GEOPHYSICAL METHODS FOR PALAEO-
INCISIONS SURVEY ON LAND
Two-dimensional (2D) common mid-point shooting and electrical
tomography, have been deployed in the Palanga–Šventoji coastal area
of Lithuania. The methods have been used separately, although
combining the interpretation of 2D seismic data with the interpretation
of electrical tomography is attempted to describe the palaeo-incisions.
43
The land part of the geophysical fieldwork has been performed
from the summer of 2012 to the spring of 2013. The productivity of
the land fieldwork is presented in Table 6.
T a b l e 6 . T i m e c o n s u m p t i o n o f g e o p h y s i c a l
m e a s u r e m e n t s .
Geophysical
method
Line Length,
m
Duration,
h
Total
length,
m
Time
consumption,
m/man-hour
2D CMP
seismic
method
S1201.1 947.5 12.0
6882.5 51
S1201.2 1747.5 19.0
S1202.1 597.5 5.0
S1202.2 897.5 9.0
S1203 1947.5 18.0
S1306 745.0 4.0
Electrical
tomography
ET-1 762.0 14.0
2580.0 28 ET-4 762.0 12.0
ET-5 1056.0 20.0
3.2.1 The 2D common mid-point (CMP) seismic method
The contrast of seismic velocities (Table 3), theoretical aspects of
shallow seismic surveys (Boganik, Gurvich 2006), and advanced
employment of 2D deep seismic methods in Lithuania, are the reasons
of choosing the 2D CMP seismic method to locate palaeo-incisions on
land.
Equipment. The CMP seismic investigations have been performed
having used a Wireless Seismic Acquisition System with 100
geophones, namely GS-ONE (manufacturer OYO Geospace, open
access facility in the Klaipėda University). A Magellan ProMark 3
GPS navigator with accuracy of 0.1 meter is used for the positioning.
The main part of the equipment is Geospace Seismic Recorder (GSR).
Its basic specifications: built-in GPS, flash memory 16 Gb, about 30
days of continuous recording (depend on environment conditions),
<20 µsec of UTC (GPS clock), selectable gain up to 36 dB and
44
recording sample intervals: 0.25, 0.5, 1.0, 2.0, 4.0 ms. Li-On battery
BX10 of 9.9 Ah and 16V is used as power supply.
Total length of 6 seismic lines is 6882.5 m (Table 6, Fig. 20).
Fig. 20 A: Location of land seismic lines. B: Location of electrical
tomography lines. 1 – 2D CMP seismic lines; 2 – lines of electrical
tomography; 3 – wells (Appendix 1).
The 2D CMP method has been performed in following steps:
Calculating theoretical parameters of field survey;
Field surveying;
45
Data processing;
Analyzing geological information from the wells;
Interpreting the seismic data.
Calculating theoretical parameters of field survey. During
common mid-point (CMP) profiling, it is arranged that a set of seismic
traces recorded at different offsets contains reflections from a common
depth point (CDP) on the reflector. When n traces containing a
mixture of coherent in phase signals and random (incoherent) noise
are stacking, the quality of signal theoretically is improved by square-
root from n. This makes it possible to attenuate long-path multiple
reflections and also to increase signal/noise ratio. Data are collected
along survey lines in 2D surveys (Kearey et al. 2002).
The depth reached with the CMP method is about 1/2–3/2 of the
maximum offset (Boganik, Gurvich 2006). Field tests show that the
maximum offset, which could be chosen, is 200–300 meters, having
used a 5 kg sledge hammer as seismic source in the area of
investigations. Therefore, the estimate depth of the method, as
deployed in this work, is between 100 and 450 meters.
The following seismic acquisition parameters have been selected:
symmetric spread with the maximum offset of 300 m, seismic station
spacing 5 m (max 61 channels), seismic source spacing 10 m and
seismic source grouping of 16 (seismic source grouping of reference
profile is 32 and seismic station spacing is 10 m across the well) (Fig.
21).
Field surveying. The length of the seismic record was 500 ms, the
sampling rate 0.5 ms and the frequency range 0-2000 Hz. The
synchronization between the seismic source and receivers was
provided by a built-in GPS.
46
Fig. 21 Reflected ray configuration of CMP investigations. 1 – Seismic
station and seismic source; 2 – seismic station; 3 – theoretical direction of
reflected ray path in the geological layer with the seismic velocity V1; 4 –
theoretical direction of reflected ray path in the geological layer with the
seismic velocity V2; 5 – geological layers of different seismic velocity.
The Source Decoder Recorder (SDR) captures the time and precise
position of each seismic source, and GSR – of each seismic record
with their internal GPS receivers. For synchronization between signal
source and record, the sledge hammer is connected to SDR with a
twin-wire cable. SDR registers the GPS time of short-circuiting at the
moment of the seismic impulse (the hit of sledge hammer).
Data processing. The seismic data processing has been performed
having applied Landmark ProMAX software with the following
procedures: trace editing and killing, summing, true amplitude
recovery, air blast attenuation, surface wave noise attenuation,
multiple wave attenuation, F-K filtering, predictive deconvolution,
band pass filtering (35-40-100-120 Hz), velocity analysis, normal
move out correction (NMO), elevation static corrections, autostatics,
dip move out correction (DMO) and migration. All the seismic
sections are the result of final data processing. The datum of all the
seismic lines is 0 m in absolute values.
47
Analyzing geological information from the wells. The geological
information from wells 573, 2868, 8592, 8594, 8634, 9870, 11248,
11249, 19622, 19623, 19631, 19657, 20084, 25027, 25513, 25992 and
25993 (Fig. 20A, B; Appendix 1; Lithuanian Geological Survey
database (2014 10 01): http://www.lgt.lt/zemelap/main.php?sesName
=lgt1412160593), and the reference seismic line S1306 provide the
basis of land seismic data interpretation. The palaeo-incision is
detected by the well 19623. The well 19623 is located on seismic line
S1306 (Fig. 20B). That is the reason, S1306 is chosen as a reference
line. The interpolated data from all the above wells have been used to
establish top depth of Quaternary, Triassic, Permian, Carboniferous
and Devonian deposits.
Theoretical aspects. Interval seismic velocity is the constant
velocity of a single layer or any fixed depth interval:
, where – top depth of the geological layer or any
fixed depth interval, – corresponding time by seismic or VSP data
(Boganik, Gurvich 2006). [1]
In its turn, seismic RMS velocities are calculated from the seismic
datum to the depth of interest as follows:
√(
), where vi – interval velocity, – time
(Boganik, Gurvich 2006). [2]
Interpreting the seismic data. Based on the well data, and the
results of earlier investigations, it is presumed, that the palaeo
channels cut into Triassic and Permian sedimentary rocks.
The general criterion for locating palaeo-incisions by the seismic
record is the differences in seismic reflectivity pattern within the
incision in relation to the surrounding bedrock. The secondary
criterion is the termination of distinct seismic events at the boundary
between a palaeo-incision and the surrounding bedrock, phase shift
and also increased amplitude of seismic events within the incision
(Table 5, Fig. 22B).
48
Fig. 22 Seismic line S1306. A: Interpreted boundaries of the palaeo-
incision; B: Interpretation. 1 – glacial deposits; 2 – aqua-glacial
deposits; 3 – inferred seismic boundary; 4 – seismic boundary; 5 –
palaeo-incision by seismic data; 6 – well (see Table 3); 7 – clay; 8 –
limestone; 9 – marlstone; 10 – sandstone; 11 - dolomite.
Locating and interpreting the seismic boundaries. There are
several distinct seismic reflections: at the times 60, 160, 200, 220, 240
and 260 ms. The most distinct seismic reflection is at the 200 ms. It is
proposed to be a top of Carboniferous by the data from the well
19623. Then the theoretical top depth of the Carboniferous is
calculated, having used the relations of interval (see [1]) and average
velocities (from the classic Mechanics) to check the hypothesis: the
Quaternary thickness plus the Permian thickness 153+11=164 m. This
value approximately equals to the value by the well data (162 m, Fig.
22). The most distinct seismic reflection at the 200 ms is concluded to
be the top of Carboniferous. The seismic reflections in the time
49
interval 200–240 ms associate with the internal reflection in the
Carboniferous strata (because of its competence by well data). All the
other seismic boundaries are associated with the corresponding tops of
geological layers from the wells 19622 and 19623 in the same way.
Seismic line S1201.2 is sub parallel to the reference seismic line
S1306. The palaeo-incision is also discovered here. It is located
between the wells 19623 and 36225, extending up to the well 19622
(Fig. 20B, Appendix 1). The turning ray tomography has been used as
an aid in the processing of the seismic data. The feature which reveals
the location of a palaeo-incision having used the interval velocity
section (as the result of turning ray tomography) is the decreasing
velocity in the deepest part of the incision (Fig. 23A).
The RMS velocity sections have been used to reach a better
understanding of the geological structures along the sections.
Analyzing the velocity section along the profile S1201.2, it is possible
to observe some zones of irregular velocities (Fig. 23B). Correlating
the sections of interval and RMS velocities, and also seismic sections,
all the seismic lines have been interpreted.
50
Fig. 23 Seismic line S1201.2. A: Interval velocity section; B: RMS velocity
section; C: Interpretation. 1 – Glacial deposits; 2 – aqua-glacial deposits; 3
– inferred seismic boundary; 4 – seismic boundary; 5 – palaeo-incision by
seismic data; 6 – wells (Table 3; Appendix 1); 7 – correlation.
51
3.2.2 Electrical tomography
In general, the electrical tomography combines the vertical
electrical sounding and the electrical profiling methods. The electrical
tomography method adapts well to the geological setting of Lithuania
for exploration of the upper part of sedimentary cover, down to depth
of 100–200 m (Šečkus 2002). For this reason the electrical
tomography method has been chosen to locate the palaeo-incisions on
land in the western Lithuania.
Resistivity methods are the means to study discontinuities in the
electrical properties of rocks, and also to detect anomalous electrical
conductivity patterns in 3D-bodies (Kearey et al. 2002).
A high resistivity contrast (Table 3), and an estimated penetration
depth of c. 150 m, has been obtained in the survey area (Fig. 20). The
previous positive experiences applying the electrical tomography
method in Lithuania is the reason to select this method as one of main
survey methods for investigation of palaeo-incisions in Lithuania.
Equipment. “Allied Tigre-128” (manufacturer UAV Survey Inc.)
has been used for the electrical tomography measurements. The field
settings used were 1 measurement per 10 seconds and c. 2600
measurements per profile. The acquisition parameters used were:
electrode spacing 6 m (128 electrodes at all), electrical field source –
36W with current rate 0.5–50 mA.
Total length of 3 electrical profiles is 2580 m (Fig. 20).
Field Survey. A schematic diagram of the electrical tomography
method is presented in Fig. 24. The electric current flows through the
commutator to the source (current) electrodes C1 and C2 (Wenner
electrode configuration). The potential difference between the values
at electrode P1 and P2 is recorded along the survey line (the spacing
between potential electrodes being fixed). Then the commutator
activates another pair of current electrodes with the same spacing
between them and potential difference is recorded along the survey
line again. After the measurements utilizing all possible (or
programmed) C1 and C2 electrodes positions with the same fixed
separation are completed, the spacing between the current electrodes
52
C1 and C2 is increased and the measuring procedure is repeated. The
theoretical measurement depth corresponds to half the C1–C2 spacing.
Fig. 24 Schematic diagram of the electrical tomography method. 1 – Current
electrodes; 2 – potential electrodes; 3 – projected points of measurements; 4
– point of measurement; 5 – inactive electrodes.
Data processing. Resistivity inversion procedure, having used the
Res2Dinv software (manufacturer Geotomo Software SDN BHD), was
performed by Dr. R. Šečkus for all the electrical lines (personal
communication).
Data interpretation. Interpretation of electrical tomography data
is a rather subjective moment. Precise detection of geological border
is possible only when the resistivity of geological layers or depths of
geological borders are known (Šečkus 2002). Theoretically (see Table
3), the resistivity of the palaeo-incision infillings should be greater
than the resistivity of the surrounding bedrock. This is because the
palaeo-incisions are cut into the Triassic clay. This theoretical
hypothesis is confirmed in practice by acquisitions of the electrical
53
tomography method across the well 19623 (Table 3). The well is
located in the center of the electrical profile ET-4, and is cased with a
metallic tube in its upper part (several meters). This may be the reason
of the lower resistivity values obtained between 390 and 440 m along
the profile ET-4 (Fig. 25). The abrupt changes in resistivity from 160
to 70 Ωm between 576 and 650 m are explained as the slope of the
palaeo-incision. The 80–160 Ωm resistivity of the palaeo-incision
body is higher than that of the enclosing rocks (70 and less Ωm).
Thus, the zone of resistivity 80–160 Ωm between 96 and 582 m of
profile ET-1 is also explained as due to the palaeo-incision (Fig. 26).
Fig. 25 Electrical tomography line ET-4. A: Measured apparent resistivity
section; B: Inverse model resistivity section. 1 – Inferred palaeo-incision; 2 –
intersection with the other line; 3 – sand, peat; 4 – till; 5 – sand, gravel; 6 –
well (see Table 3).
54
Fig. 26 Electrical tomography line ET-1. A: Measured apparent resistivity
section; B: Inverse model resistivity section. 1 – Inferred palaeo-incision; 2 –
intersection with the other line.
3.2.3 Integration and interpretation of geophysical data
The combination of the 2D CMP seismic method (positions 460–
1222 along profile S1201.2) and electrical tomography (profile ET-1)
has been used to obtain the location and details of the palaeo-incision
with an enhanced resolution (Fig. 27). First the location of the palaeo-
incision was determined by seismic data, and then by electrical
tomography data (the principles of interpretation are described above).
Next the two results were overlaid and the northern slope of the
palaeo-incision, as revealed by electrical data, was added. The main
principle of locating palaeo-incisions in seismic recordings is to use
the levels in the seismic section, where the seismic reflectivity pattern
changes, the phase of the reflection shifts or where it increases in
strength (Table 5). These places are considered to reveal the borders
between the palaeo-incisions and the surrounding bedrock. In case of
electrical tomography the contrast in resistivity properties of rocks
within and outside the palaeo-incision is used.
55
Fig. 27 Combined geophysical interpretation of lines S1201.2 and ET-1: 1 –
inferred palaeo-incision by data of electrical tomography; 2 – intersection
with the other line; 3 – glacial deposits; 4 – aqua-glacial deposits; 5 –
inferred geological boundary; 6 – geological boundary; 7 – palaeo-incision
by seismic data; 6 – palaeo-incision by electrical tomography data; 8 –
location of electrical tomography line ET-1; 9 – palaeo-incision by combined
geophysical interpretation.
56
3.3 SURVEY OF THE SUB-QUATERNARY RELIEF
New sub-Quaternary relief map has been compiled having used all
accessible new data as well as data of previous offshore works
(Repečka 1991; Gelumbauskaitė, Grigelis 1997; Gelumbauskaitė
1999), unpublished land data (Bitinas et al. 1998, 2004; Bitinas 2000,
2011, 2013; Bitinas et al. 2003) and also a schematic sub-Quaternary
surface map (Šliaupa et al. 1994).
Offshore well data provided the basic information for compiling of
the sub-Quaternary surface (Appendix 1). The wells were used as the
bench marks, for compiling of the sub-Quaternary surface during the
interpretation of seismic data. The relation between seismic data and
well data is given in Appendix 1. The seafloor and base of the
Quaternary strata were traced in the time domain across the entire
offshore part of the investigated area. The next step was to compile
the offshore sub-Quaternary surface of the investigated area in the
time domain. The obtained surface was then recalculated to the depth
domain having used a constant seismic velocity 1800 m/s (personal
communication with Professor A. Grigelis and Dr. L.Ž.
Gelumbauskaitė).
Finally, the sub-Quaternary relief map of Lithuania (Šliaupa et al.
1994), five newly mapped land segments (Bitinas et al. 1998, 2004;
Bitinas 2000, 2011, 2013; Bitinas et al. 2003) and the offshore sub-
Quaternary relief map, were imported to the Global Mapper software.
The last six segments were connected together and attached to the
sub-Quaternary relief map (Šliaupa et al. 1994) in the entire
rectangular area (21o 30ʹ – 22
o 00ʹ E, 55
o 28ʹ – 55
o 42ʹ N). Connection
in this case means joining the isolines at the boundaries of
neighboring segments. In those cases where isolines of equal depth
diverge on the two sides of a boundary, the connection was done by
interpolation. The surface of the Quaternary relief was created
applying a minimum curvature method and a grid of 100 × 100 m in
the Lithuanian LKS-94 coordinate system.
57
3.4 TECHNIQUE, APPLIED TO COMPOSE THE
SCHEME OF PALAEO-INCISIONS
First, all the segments of palaeo-incisions have been discovered in
the entire area of investigations offshore (Appendix 3). Next, the
relative width and depth of palaeo-incisions have been described. The
term relative width means in this case the visible width of the palaeo–
incision along the seismic line. The angle, differing from 90 degrees,
makes the visible width of the palaeo-incision wider.
Discovered segments of palaeo-incisions were connected in the
following cases:
- Palaeo-incisions are presented along the neighboring seismic
lines. Also it was kept to the rule, that the palaeo-incision could not
cross the seismic line without any discovered segment of palaeo-
incision along (Fig. 28 B–F).
- The shape, depth, relative width and infilling of the joining
segments are similar in general, particularly, when the palaeo-incision
is forming during several generations (Fig. 28 A, G).
Fig. 28 Main principles of composing the scheme of palaeo-incisions. 1 –
Discovered segment of palaeo-incision; 2 – seismic line; 3 – interpreted
palaeo-incision.
The orientation of palaeo-incision is known in the cases of at least
two connected segments. It corresponds to the direction of joint line
from the segment of lower depth to the deeper segment. In the other
cases, the orientation of palaeo-incisions is considered to be
conformed to the sub-Quaternary relief (Fig. 29). Knowing the
58
orientation, it is possible to determine the true angle between the
palaeo-incision and crossing seismic line in order to establish the
width of palaeo-incision more precisely. Finally, the true width has
been calculated from the relative one and tagged on the CSP data
location map.
Fig. 29 Downward trend of sub-Quaternary relief(1) and orientation of
palaeo-incisions(2): arrows show deepening direction.
The shape of palaeo-incision has been described visually,
analyzing their sections. The sections, perpendicular to the orientation
of palaeo-incisions, were preferred and were the basis of this analysis.
The palaeo channels of simple shape, incisive in the bottom part, were
assumed to be of V-shape, while those similar, but smooth in the
bottom part were of U-shape. More complex shapes were assumed to
be of W- and WW- (the most complicated visually) shapes (Table 7).
Analyzing the sections of palaeo-incisions it has been noticed, that
their depth and morphology differ in three certain segments in the
southeastern part of the Baltic Sea.
59
An attempt has been made to determine the palaeo-incisions of
several generations (blue in Fig. 30A, C–F).
T a b l e 7 . C l a s s i f i c a t i o n o f p a l a e o - i n c i s i o n s
a c c o r d i n g t o t h e i r c r o s s - s e c t i o n m o r p h o l o g y
Shape Description Example
V Two slopes;
a/b≥2
U Two slopes;
a/b<2
W Four slopes
WW More than four
slopes
The D3–D4 seismic unit is characterized by a slightly folded
stratified seismic reflectivity pattern (Fig. 30A).
The reflection from the P2 seismic unit is very intense, easily
recognized and possible to use as a seismic marker (Fig. 30B, C, D).
The main feature of the palaeo-incisions in the Triassic area (see Fig.
2), as compared to the Devonian area, is the contrast between seismic
reflectivity patterns inside the incisions in relation to the surrounding
bedrock areas (Fig. 30E, F, G). The palaeo-incisions often exhibit
strong reflections crossing over the reflection multiple of the sea floor
in the eastern zone (Fig. 30B). Furthermore, breaks in strong and
60
enduring bedrock reflections often facilitate the identification of
palaeo-incisions here (Fig. 30D, F, H).
Land network of palaeo-incisions has been composed having used
the data of earlier geological mapping (Bitinas et al. 1998, 2004;
Bitinas 2000, 2011, 2013; Bitinas et al. 2003). Palaeo-incisions were
joined on the boundaries of neighboring mapped segments. For those
cases where two palaeo-incisions similar by morphology and depth
diverge on the two sides of a boundary, the connection was done by
interpolation.
Land network of palaeo-incisions were joined to the offshore one
hypothetically. The main principle was the direction of the palaeo-
incisions.
61
Fig. 30 Fragments of seismic lines: A – 980903_2; B – 980818_2; C – 9522;
D – 980830_5; E –980829_3; F – 9405; G – 9410B; H – 980830_5(three
palaeo-incisions). Location see Fig. 31. Blue – inferred palaeo-incision,
white – palaeo-incision.
62
3.5 COMPILATION OF THE PRE-QUATERNARY
GEOLOGICAL MAP
Combining the seismic interpretations of earlier expeditions
(Grigelis et al. 1994, 1996) with the last one it became possible to
update the pre-Quaternary geological map of the investigated area.
This map is based on the map elaborated by Algimantas Grigelis in
1998 as a part of the Geological map of the Northern Europe land and
seas areas (Sigmond 2007). It was later modified by Grigelis in 2012
(personal communication). A number of data sets were used for the
new interpretation, namely well data (Figs. 16–19; Appendix 1),
earlier interpretation of the seismic lines 9302, 9404, 9405 and 9410
(Fig. 15), seismic stratigraphic subdivisions: Late Devonian seismic
units D3–D4 (Flodén 1980) and from Late Permian P2 to Late
Cretaceous K2 seismic units (Grigelis 1999) (Table 8). The seismic
data interpretation starts with the seafloor across the entire
investigated area, and is then extended downwards to the deepest
seismic boundary in a similar manner. This method has been chosen in
order to make a correct tracing of seismic boundaries and conversion
to seismic units, particularly in the places of complex seismic
reflectivity patterns. Eight surfaces, corresponding to the top of
seismic units (including the top of pre-Quaternary surface) were
defined, based on seismic data.
The result was exported to Global Mapper software. There it was
united with the previous geological map of the southeastern segment
of the Baltic Sea (Fig. 2; after Grigelis 2009, modified in 2012
(personal communication)) in the area framed by 20o 50ʹ – 22
o 00ʹ E.
Finally, the area framed by 21o 00ʹ – 22
o 00ʹ E updated having used
the newest data of geological mapping (Bitinas et al. 1998, 2004;
Bitinas 2000, 2011, 2013; Bitinas et al. 2003).
63
T a b l e 8 . V a l u e s o f s e i s m i c v e l o c i t i e s i n
l i t h o l o g i c a l - s t r a t i g r a p h i c c o m p l e x e s o f t h e
B a l t i c S e a .
Age of
complexes
Layer
velocity1,
m/s
Interval
velocity2,
m/s
RMS
velocity2,
m/s
Chosen
velocity, m/s
Water layer 1438 – 1446 — — 1440
Quaternary 1700 – 1850 — — 1800
Paleogene–
Neogene 1950 — — —
Cretaceous 2000 — — 2000
Late Jurassic
2100
— — 2050
Middle
Jurassic — — 2150
Triassic 2350 4565 1835 2350
Permian 2200 – 5000 3940 2005 2400
Carboniferous 2500
— — —
Devonian 3060 2450 2500
Silurian 3000 3365 2745 —
Ordovician 3500 4340 2885 —
Cambrian 2750 4270 2945 — 1 — Grigelis 1999;
2 — by VSP data from well D5 (location see Fig. 14).
4. RESULTS
4.1 THE SUB-QUATERNARY RELIEF
The scheme of palaeo-incisions have been composed on the
background of the pre-Quaternary relief with the number of regional
64
morphostructures determined during the previous investigations
(Gelumbauskaitė 1995; Šliaupa 2004), i.e. the Eastern Gotland
Through in the northwest (I), the Klaipėda–Liepaja Uplift in the west
central part (II), the Gdansk Depression in the southwest (III), the
Curonian structural terrace in the southeast (IV), the Telšiai swell in
the northeast (V) and Western Žemaitija step in the west (VI) (Fig.
31).
The palaeo-incision network of the investigated area is divided into
three parts, namely eastern zone (3 in Fig. 31), central zone (4 in Fig.
31) including northern part of the Gdansk Depression and its Klaipėda
Slope, and western zone (5 in Fig. 31) including eastern slope of the
Gotland Depression. The names of the zones are chosen according to
their geographical location within the investigated area.
Level of the sub-Quaternary surface in the Eastern Gotland
Through varies from –150 m to –60 m in the southeastern direction.
The palaeo-incisions of the western zone (5 in Fig. 31) cut the sub-
Quaternary surface down to –280 m in absolute values. Five
fragments of palaeo-incisions are newly discovered in the deepwater
zone.
The Klaipėda-Liepaja Uplift separates deepwater and central zones
of palaeo-incisions. Palaeo-incisions of the central zone (4 in Fig. 31)
cut the sub-Quaternary surface down to –200 m in absolute values.
The absolute values of the sub-Quaternary surface vary from –60 m at
the Klaipėda–Liepaja Uplift to –100 m in the direction of the Gdansk
Depression. Forty-five new fragments of palaeo-incisions were
discovered, which include twenty-five in the northern part of the
central zone (4 in Fig. 31). This means that the network of palaeo-
incisions is wider and more complicated, than it has been presumed
earlier.
65
Fig
. 3
1 T
he
ma
p o
f p
ala
eo-i
nci
sio
ns
on
th
e su
b-Q
ua
tern
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su
rfa
ce.
1 –
con
tou
r li
nes
of
the
sub
-Qu
ate
rna
ry
surf
ace
(d
raw
n e
very
10
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Lit
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an
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; 3
– e
ast
ern
zo
ne
of
pa
laeo
-in
cisi
on
s; 4
– c
entr
al
zon
e
of
pa
laeo
-in
cisi
on
s; 5
– w
este
rn z
on
e o
f p
ala
eo-i
nci
sio
ns;
6 –
pa
laeo
-in
cisi
on
on
lan
d(B
itin
as
et a
l. 1
99
8,
20
04;
Bit
ina
s 2
00
0, 2
011
, 20
13
; B
itin
as
et a
l. 2
003
); 7
– i
nfe
rred
pa
laeo
-in
cisi
on
s; 8
– r
ela
tive
dep
th o
f n
ewly
dis
cove
red
pa
laeo
-in
cisi
on
s in
met
ers;
9 –
rel
ati
ve d
epth
of
con
firm
ed p
ala
eo-i
nci
sio
ns
in m
eter
s; 1
0 –
fra
gm
ents
of
seis
mic
lin
es (
Fig
s. 1
5 –
19
, 3
2 –
34
).
66
The eastern zone of palaeo-incisions is divided into two separate
parts by the 56o N parallel, here referred to as the northern and the
southern parts (3 in Fig. 31). The absolute depth of the sub-Quaternary
surface varies from –10 m to –60 m and the depth of the palaeo-
incisions – from –65 m to –130 m in the northern part of the eastern
zone. Two fragments of palaeo-incisions, discovered by other
investigators previously, have been confirmed, and fourteen new
fragments have been discovered there. The absolute depth of the sub-
Quaternary surface is from –40 m to –80 m in the southern part of the
eastern zone. In absolute values, the depth decreases from South to
North, but it increases again to –80 m at the northwestern slope of the
Curonian structural terrace. The depth of palaeo-incisions varies from
–60 m to –140 m. Three previously mapped palaeo-incisions have
been confirmed, and seventeen new palaeo-incisions have been
discovered there. The shape of the seafloor and the sub-Quaternary
surface is more different near the coastline as compared to the results
of earlier investigation.
The level of the sub-Quaternary surface on land varies from sea
level in the northeast and southeast to –60 m in the southwestern
direction. The palaeo-incisions prevail near the coastline and in the
northwestern land areas.
Generally orientation of palaeo-incisions and downward trend of
sub-Quaternary relief are corresponding. As mentioned above, the
main directions of deepening are the Telšiai swell – the Eastern
Gotland Through, Western Žemaitija step – the Gdansk Depression,
the Klaipėda-Liepaja Uplift – the Gdansk Depression and the
Klaipėda-Liepaja Uplift – the Eastern Gotland Through (Fig. 29, 31).
To summarize, eighty-two new fragments of palaeo-incisions have
been discovered in the offshore part of the investigated area (Fig. 31,
Appendix 3). First of all, the new fragments, found during the new
investigation, made it possible to reconstruct the network of palaeo-
incisions. Secondly, the palaeo-incisions have wider distribution in the
offshore part of Lithuania, and also exhibit a more complicated
pattern, than previously assumed (Fig. 7). The newly compiled sub-
Quaternary surface map generally corresponds to the earlier one. But
67
there are some differences. Maps primarily do not match near the
shore and in the central zones. It is due to inclusion of the new
mapping data from the coast and denser network of seismic lines,
including the more recent seismic data used in this part of the
investigated area.
4.2 MORPHOLOGY AND NETWORK OF PALAEO-
INCISIONS
The distribution of palaeo-incisions is irregular in the entire area of
the investigations. But there are zones, where it is possible to
generalize their relative depth, width and shape. This generalization is
the principle of dividing the network of palaeo-incisions into three
parts, namely the eastern zone, the central zone and the western zone
(Fig. 31).
The relative depth of the palaeo-incisions below the bedrock
surface ranges from 23 to 153 m. It increases from shore area to the
deep-water area.
The width of the palaeo–incisions varies in the interval of 240 –
7220 m. The average width decreases from the eastern zone (2340 m),
through the central zone (1460 m) to the western zone (960 m).
The distribution of palaeo–incisions by shape changes from quite a
few complicated W- and WW-shapes in the eastern zone to the
prevailing of trivial V-shapes in the deepwater zone. No palaeo-
incisions penetrated into the sub–Quaternary surface of the Klaipėda–
Liepaja Uplift have been identified.
The palaeo–incisions in the eastern zone predominantly extend in
the ENE to WSW direction (Fig. 29). The visible lengths of the
palaeo–incisions are about 20–25 km. Towards the NNE they do
simply terminate, whereas towards the SSW they generally merge
together (Fig. 31). The palaeo-incisions in this zone are generally
rather shallow reaching relative depth of 23–80 m into the bedrock.
Their average depth is about 50 m (Fig. 31). W- and WW-shapes are
widely distributed accounting for 53% of the analyzed incisions (W-
68
shape 36%, WW-shape 17%). V- and U-shapes comprise the remains:
V-shape 28% and U-shape 19% respectively (Appendix 3). Wide
palaeo-incisions, with widths of more than 2000 m, occur frequently
in this zone. The network of palaeo-incisions in the eastern zone forms
several isolated groups of palaeo-incisions. The palaeo-incisions cut
Late Permian–Early Triassic strata in the northern part and Early
Triassic–Late Jurassic strata in the central–southern part.
The incisions in the northern part of the central zone extend from
northeast to southwest and from north to south. The distribution of the
palaeo-incisions in the southern part is more complicated (Fig. 31).
The palaeo-incisions of the central zone (northern part of the Gdansk
Depression and its Klaipėda Slope) extend to relative depth of 27–113
m into the bedrock, at an average about 80 m (Fig. 31). Palaeo-
incisions of various shapes are presented in this zone. The V-shape
dominates to 44%, whereas the U-shape is also widely distributed to
33%. The majority of remaining incisions (23%) demonstrates W-
shape in cross-section (Appendix 3). The width of the palaeo-incisions
varies widely, from 340 m to 7220 m. The palaeo-incisions form
single complicated (shape-wise) system in the central zone. The
palaeo-incisions cut Late Permian–Late Jurassic sedimentary strata in
this zone.
The palaeo-incisions of the western zone, namely the eastern
slope of the Gotland Depression, mainly traverse from northwest to
southeast. Towards the north and west they continue outside the area
of investigations. The length of two main incisions is about 42 km
inside the investigated area (Fig. 31). This is the zone with the deepest
palaeo-incisions. Their relative depth is in the range of 53–153 m into
the bedrock with an average depth of about 100 m (Fig. 31). The V-
shape dominates in the cross-sections to 73% in this zone (Appendix
3). The width of the palaeo-incisions is between 300 and 1760 m. This
zone is separated from the central zone by the structural high of the
Klaipėda-Liepaja Uplift. The palaeo-incisions are of NW–SE
orientation. The palaeo-incisions form system, which is close by shape
to the river network in this zone. The palaeo-incisions cut Late
Devonian strata in this zone.
69
All the palaeo-incisions cut the Quaternary strata. The Quaternary
thickness varies from 1–5 m in the western zone, to 20–40 m in the
central zone and reaches up to 50–60 m in the eastern zone.
T a b l e 9 . R e l a t i o n s h i p b e t w e e n s h a p e s a n d
s u r r o u n d i n g b e d r o c k o f p a l a e o - i n c i s i o n s .
All the investigated area
Shape, pcs
Su
rro
un
din
g
bed
rock
U V W WW
tota
l
D3 4 11 2 – 17
P2 6 11 13 2 32
T1 20 28 22 6 76
J2 19 22 12 5 58
J3 14 16 6 3 39
Central zone
Shape, pcs
Su
rro
un
din
g
bed
rock
U V W WW
tota
l
D3 3 3 – – 6
P2 4 7 5 1 19
T1 15 21 9 1 46
J2 14 17 8 – 39
J3 9 11 3 – 23
Eastern zone
Shape, pcs
Su
rro
un
din
g
bed
rock
U V W WW
tota
l
P2 2 4 8 1 15
T1 5 7 13 5 30
J2 5 5 4 5 19
J3 5 5 3 3 16
Western zone
Shape, pcs
Su
rro
un
din
g
bed
rock
U V W WW
tota
l
D3 1 8 2 – 11
The relationship between shapes and surrounding bedrock of
palaeo-incisions is analyzed in this work (see Table 9). The palaeo
channels of V-, U- and WW-shape, cut into Late Permian sedimentary
rocks, are distributed similarly in percentage correlation within the
70
central and eastern zones. The palaeo channels of W-shape, cut into
Late Permian–Early Triassic strata, dominate within the eastern zone
to about 50%. The palaeo-incisions of WW–shape cut Early Triassic–
Late Jurassic strata and dominate in the eastern zone. The V- and U-
shape dominate to 80% among the palaeo-incisions cut into Early
Triassic–Late Jurassic strata in the central zone. The palaeo channels
of V-, U- and W-shape, cut into Middle–Late Jurassic sedimentary
rocks, are distributed similarly in percentage correlation within the
central and eastern zones. The palaeo-incisions of W-shape occur
rarely in the Late Devonian strata. Only two of them found in the
entire area. The majority (65%) of palaeo-incisions cut into these
rocks are V-shaped.
The distribution of V- and U-shapes is similar in percentage
correlation for Late Permian–Late Jurassic rocks in the central and
eastern zones (Table 9). Also the V-shape of palaeo-incisions within
Late Devonian strata dominates in the entire area of investigations.
4.3 INFILLING OF PALAEO-INCISIONS OFFSHORE
The infillings of the palaeo-incisions are widely different and
complex. The Quaternary section of the southeastern Baltic Sea has
been evaluated from 17 vibrocores and short drill cores (see Appendix
1) applying lithological–biostratigraphical and radiometric methods
(Majore et al. 1997; Gelumbauskaitė 2000, 2009). The penetration
into the Quaternary depositional complex in the short drill cores varies
from 4 to 10–20 m. Thirteen of the deep wells (Figs. 32–34, Appendix
1) disclose the Quaternary section in full. The relative depth of the
palaeo-incisions ranges from approximately 50 in the near shore area
to around 100 m in the deepwater area. In the deepwater areas there
are generally five different erosional and depositional units found in
the incisions, whereas in the near shore shallow areas there are only
two or three (Bjerkéus et al. 1994). Some of palaeo-incisions contain
indications of merely one or two of the above depositional events
(Vaher et al. 2010; Janszen et al. 2013). The infillings generally
71
contain several sediment types, namely glacial, glaciofluvial and
glaciolacustrine sandy–clayey deposits, till and gravel as reported
from Lithuania (Bitinas et al.1999), Estonia (Vaher et al. 2010),
Sweden (Bjerkéus 1998), and Germany (Janszen et al. 2013).
Fig. 32 Fragment of seismic line 980830_1. A: Geological section; B:
Interpretation. 1 – sand; 2 – mud; 3 – silt; 4 – clay; 5 – Till-1; 6 – Till-2; 7 –
Till-3; 8 – bedrock; 9 – geological boundaries; 10 – geological boundaries
within the Quaternary strata; 11 – palaeo-incision; 12 – seafloor; 13 – well
(location see Fig. 14); 14 – seismic unit of palaeo-incision infilling.
Seven seismic units (A–G) of palaeo-incision infilling, including
three types of tills, namely Till-1, Till-2 and Till-3, are classified
based on the well data and internal seismic reflectors in the area of
investigation (Table 10, Figs. 32–34).
Unit A. Seismic reflectivity pattern is described by coherent
distinct and strong seismic events (Fig. 32, 110–120 ms; Fig. 34, 40–
50 ms). This unit is associated with layers of sand and gravel.
Unit B. Seismic reflectivity pattern is characterized by sub-
coherent and rather strong seismic events, although weaker compared
to unit A (Fig. 32, 120–130 ms; Fig. 33, 90–120 ms). This unit is
associated with mud.
Unit C. Seismic reflectivity pattern is rather homogeneous with
some irregularities (Fig. 32, 130–140 ms and 170–180 ms; Fig. 33,
140–150 ms). This seismic unit is connected to silt.
72
T a b l e 1 0 . S u b d i v i s i o n o f p a l a e o - i n c i s i o n
i n f i l l i n g : s e i s m i c u n i t s A – G .
Seismic
unit
Description of
seismic reflectivity
pattern
Geological
interpretation
Typical example
A Coherent distinct and
strong seismic events
Sand and
gravel
B Sub-coherent and
rather strong seismic
events, weaker
compared to unit A
Mud
C Rather homogeneous
seismic events with
some irregularities
Silt
D Rare, wide and
comparatively
coherent seismic
events
Clay
E High-dip incoherent
reflections with
distinct fragments of
seismic events
Till-1
F Almost homogenous
seismic events with
rare amorphous
reflections
(‘semi-transparent’)
Till-2
G Coherent, thin and
irregular seismic
events with some
noise
Till-3
73
Fig. 33 Fragment of seismic line 980901_2. A: Geological section; B:
Interpretation. 1 – Mud; 2 – silt; 3 – clay; 4 – Till-1; 5 – Till-2; 6 – Till-3; 7
– geological boundaries; 8 – geological boundaries within the Quaternary
layer; 9 – palaeo-incision; 10 – seafloor; 11 – well (location see Fig. 14); 12
– seismic unit of palaeo-incision infilling.
Fig. 34 Fragment of seismic line 9405. A: Geological section; B:
Interpretation. 1 – sand; 2 – Till-1; 3 – Till-2; 4 – bedrock; 5 – geological
boundaries; 6 – geological boundaries within the Quaternary layer; 7 –
palaeo-incision; 8 – seafloor; 9 – well (location see Fig. 14); 10 – seismic
unit of palaeo-incision infilling.
Unit D. Seismic reflectivity pattern is marked by rare, wide and
comparatively coherent seismic events (Fig. 32, 140—150 ms; Fig.
33, 110—130 ms). It is associated with clay.
74
Unit E. Seismic reflectivity pattern is described by high-dip
incoherent reflections with distinct fragments of seismic events (Fig.
32, 150–170 ms; Fig. 33, 130–140 ms). This unit is associated with
Till-1.
Unit F. Seismic reflectivity pattern is almost homogenous, with
rare amorphous reflections (“semitransparent”) (Fig. 33, 170–200 ms)
or incoherent reflections with small fragments of seismic events (Fig.
34, 70—90 ms). This unit is connected to Till-2.
Unit G. Seismic reflectivity pattern is described by coherent, thin
and irregular seismic events with some noise (Fig. 30A, 290–340 ms).
This unit is associated with Till-3.
The lowermost three units are separated by erosional surfaces
creating strong contrast and, thus, strong seismic events within the
palaeo-incision (Fig. 32, 180 ms; Fig. 33, 150 ms; Fig. 34, 50 ms; Fig.
30A, 270 ms and 320 ms). In consequence of this fact, distinct seismic
borders within the palaeo-incisions and between different types of
seismic reflectivity patterns correspond to erosional surfaces dividing
between different types of tills.
Based on the foregoing relationship between seismic reflectivity
pattern and type of deposits, about one hundred seismic sections
crossing palaeo-incisions have been analyzed (see Appendix 3, Table
11). Seven different types of deposits, described above as units A–G
have been found in the palaeo-incisions.
Layers of sand and gravel (unit A) are absent in the northern part of
the central zone (Fig. 31) and truncated across the entire part of the
investigated area. The average thickness of unit A deposits is about 10
m, minimum is about 4 m and maximum is about 30 m in the western
zone. Generally the thickness of these infilling increases from shore
area to the western zones (Fig. 31). Clay (unit D) disappears in the
northwestern direction.
Till-1 (unit E) is abundant across the entire area. The thickness of
the Till-1 is between 5 and 50 m, with a mean thickness of about 20
m. Till-2 (unit F) is locally absent in the central and eastern zones.
75
T a b l e 1 1 . S t a t i s t i c a l d a t a a b o u t i n f i l l i n g o f t h e
p a l a e o - i n c i s i o n s .
All the investigated area
Thickness, m
Seismic unit A A2 B C D E F G
Min 3.6 7.2 2.7 6.3 2.7 5.4 5.4 7.2
Max 29.7 27.0 10.8 21.6 26.1 47.7 46.8 45.9
Average 11.6 12.4 7.4 12.5 12.3 18.9 20.5 21.7
Western zone
Thickness, m
Seismic unit A A2 B C D E F G
Min 9.9 9.9 — 12.6 7.2 5.4 7.2 16.2
Max 29.7 27.0 — 21.6 20.7 47.7 39.6 45.9
Average 19.3 15.9 — 16.7 12.7 20.1 24.7 32.9
Eastern zone
Thickness, m
Seismic unit A A2 B C D E F G
Min 3.6 7.2 — 6.3 2.7 7.2 5.4 7.2
Max 16.2 12.6 — 14.4 17.1 42.3 40.5 28.8
Average 8.9 10.4 — 10.7 9.0 19.3 17.9 18.8
Central zone
Thickness, m
Seismic unit A A2 B C D E F G
Min 6.3 10.8 6.3 7.2 6.3 6.3 9.0 7.2
Max 23.4 15.3 10.8 19.8 26.1 42.3 46.8 36.9
Average 11.2 12.4 8.1 12.1 13.5 18.3 21.1 20.0
76
The mean thickness of the Till-2 is about 20 m, with its minimum
being about 5 m, and maximum about 45 m in the northern part of the
central zone. Till-3 (unit G) is presented in about 50% of the
investigated palaeo-incisions in the eastern zone. They are also locally
absent in the central zone. But they are abundant across the entire
western zone. The thickness of the Till-3 is between 7 and 45 m, with
the mean thickness being about 20 m. The quantity of till deposits
increases from the eastern zone to the western zone. The thickness of
sediments associated with the units A–F increases also in the direction
of the southern part of central zone (northern part of Gdansk
depression), but unit B is found only in the central zone, and unit C
reaches its maximum thickness in the western zone.
To summarize, based on analysis of internal seismic reflectors,
seven types of deposits have been classified in infillings of palaeo-
incisions in the entire area of investigations (see Appendix 3).
4.4 THE PRE-QUATERNARY GEOLOGY
In a general way, the investigated area may be divided into four
parts according to bedrock outcropping on the sub-Quaternary surface:
the northwestern, the northeastern, the southeastern and the southern
one. The Late Devonian layered sedimentary rocks crop out on the
sub-Quaternary surface in the northwestern part of the investigated
area, the Early Triassic–Late Jurassic sedimentary rocks – in the
north-eastern part, the Late Permian–Late Jurassic – in the
southeastern part and the southern part is covered by Cretaceous
sedimentary strata (Fig. 35). The outcrops of the Early Triassic
sedimentary rocks “cut” the Middle Jurassic ones along palaeo-
incisions in the northeastern part. The central part is raveled by
outcrops of the Late Devonian–Middle Jurassic within palaeo-
incisions. Examples of the geological sections are presented in Figs.
36–38. A comparison between the new bedrock map and the previous
one is presented in Fig. 36.
77
Fig
. 3
5 T
he
pre
-Qu
ate
rna
ry g
eolo
gic
al
map
of
the
sou
th-e
ast
ern
Ba
ltic
Sea
: 1 –
La
te C
reta
ceo
us;
2 –
Ea
rly
Cre
tace
ou
s; 3
– L
ate
Ju
rass
ic;
4 –
Mid
dle
Ju
rass
ic;
5 –
Ea
rly
Tri
ass
ic;
6 –
La
te P
erm
ian
; 7
– L
ate
Dev
on
ian
(Fra
snia
n);
8 –
co
nto
ur
lin
es o
f th
e su
b-Q
ua
tern
ary
su
rfa
ce (
dra
wn
eve
ry 1
0 m
); 9
– t
he
Lit
hu
an
ian
Sea
bo
rder
; 1
0 –
wel
ls (
see
Ap
pen
dix
1);
11
– g
eolo
gic
al
sect
ions
(see
Fig
s. 3
7 –
39
).
78
Fig. 36 Comparison of geological maps. A: Bedrock geology of the
southeastern Baltic Sea (after Grigelis 2009, modified 2012); B: Bedrock
geology of the southeastern Baltic Sea by D. Gerok, 2014.
79
Fig. 37 Geological section. Fragment of seismic line 9404 (for location see
Fig. 14).
Fig. 38 Geological section. Fragment of seismic line 980830_5 (for location
see Fig. 14).
Fig. 39 Geological section. Fragment of seismic line 980901_3 (for location
see Fig. 14).
80
The new investigation reveals that Middle Devonian outcrops are
absent on the sub-Quaternary surface in the northwestern part of the
investigated area contrary to earlier works (A in Fig. 36). This fact is
confirmed by the 1998-1999 seismic data, which are more recent than
those used for compiling of the earlier map.
Late Permian sedimentary rocks crop out on the sub-Quaternary
surface in the central part of the investigated area and there are some
fine details connected to palaeo-incisions in the northeastern part as
well. The Late Permian outcrops in the central part of the area
coincide in general with the earlier map. New outcrops of Late
Permian have been confirmed on the sub-Quaternary surface in the
central part of the investigated area.
In general, the Early Triassic outcrops conform to the earlier map,
but its northern boundary extends further to the west than presumed
previously. Also, the new details associated with palaeo-incisions are
added in the northeastern part of the investigated area.
Denser network of seismic lines, including the data of the 1998–
1999 expeditions, revealed the presence of Middle Jurassic outcrops in
the offshore part of the investigated area for the first time. Moreover,
the new geological mapping on land provided the new details of
geological boundaries in the northeastern part of the investigated area.
The outcrops of the Late Jurassic sedimentary rocks also conform
in general to the earlier map. They are abundant in the larger part of
the offshore area and in a small area on land as results of the new
investigation there. There are also the new details in the map
connected to palaeo-incisions in the southeastern part of the
investigated area.
Outcrops of the Cretaceous conform between the maps in the
offshore part of the investigated area, but there are some new details
connected to palaeo-incisions in the southeastern part on land.
In conclusion, the outcrops of the Early Triassic, the Late Jurassic
and the Cretaceous sedimentary rocks coincide in general with the
results of the earlier investigation. Outcrops of the Middle Devonian,
as known in the older map, are not verified, but new outcrops of the
Late Permian and the Middle Jurassic are found in the area of
81
investigation (Fig. 36). Usage of the new geological mapping on land
and the seismic data offshore (1998-1999 expeditions) provided the
new details of the Late Devonian–Late Cretaceous outcrops (except
the Cretaceous offshore). Moreover, the fine details, connected to
palaeo-incisions are added to the geological knowledge of the
investigated area.
5. DISCUSSION
5.1 INTERPRETATION OF GEOPHYSICAL DATA
The depth penetration of the CMP seismic method proved
sufficient to locate even the deepest parts of palaeo-incisions, but it
proved difficult to describe in any detail the upper geological
boundaries due to the fuzziness of seismic section there. Sometimes
turning ray tomography procedures and sections of root-mean-square
velocities allowed solving this problem. A seismic source grouping of
32, was used for the reference profile (Fig. 22B), showed a superior
result compared with a grouping of 16 (Fig. 23C). Probably it is also
necessary to increase the CDP fold having used smaller source
spacing for better results in the future. It is only possible to use the
shallow seismic method to locate the buried valleys under these
conditions. The productivity is about 25 m per man-hour in this case
(see Table 6).
Electrical tomography, as it was anticipated, can be used to locate
the slopes of palaeo-incisions. It proved impossible to get the full
information of the palaeo-incision shape, however. Equipment should
be of deeper penetration for better result. Applying this method alone
is not sufficient to identify the location of palaeo-incision, i.e. if the
profile is located along a palaeo-incision or if the width of the palaeo-
incision is greater than the profile. Therefore different electromagnetic
methods with deeper penetration should be tested. Usage of the
methods with deeper penetration might help to solve this problem.
82
Gravimetric surveys previously performed in the Lithuanian
coastal area, with the above mentioned results for the Dovilai area,
show that the method is useful and it could be added as an additional
method into the described complex of geophysical methods for
prospecting of palaeo-incisions. For example, it could be useful for
locating potential palaeo-incisions for future investigations.
The complexity of the CSP data interpretation involves several
aspects. The first limiting factor is that only a few deep offshore wells
are accessible within the investigated area (see Appendix 1). The
second limiting factor is connected to complicated composition of the
Quaternary glacial deposits. The next problem is the water depth of
the investigated area. Multiple reflections from the seismic boundaries
are most often very intense and overprint the reflections of deeper
seismic boundaries in the shallow areas. This is the reason, the
shallow water part is less investigated in the entire area. It is possible
to solve this problem having used multichannel equipment and
common deep point (CDP) seismic method in the shallow water.
The deepest parts of palaeo-incisions (3 in Fig. 31) are often deeper
than the multiple seismic reflections from the seafloor in the eastern
zone. Supposedly, this is the reason why unit G is only found in a half
of investigated palaeo-incisions there. The seismic reflectivity pattern
of this unit might be described in different ways according to the data
digitizing quality and the local area. But it seems possible to
understand the quantity of palaeo-incision generations by their
erosional surfaces, which associate with high contrast and strong
seismic events within palaeo-incisions.
The fact that the infilling of palaeo-incisions often has up to three
depositional events, might indicate that some channels are
successively reopened, possibly even during each glaciation. Thus,
due to differences in the infillings, it is presumed, that there are at
least three generations of palaeo-incisions formed during three
different glaciations. The younger generations cut into the soft
sedimentary bedrock or into the infilling of older palaeo-incisions. In
general the palaeo channels of older generations are deeper than the
younger ones (Bjerkéus et al. 1994). An attempt has been made to
83
show this with inferred boundaries within the palaeo-incisions (Fig.
30A, C–F). But because the contrast of seismic reflectivity pattern is
rather low, these details are only assumed. More precise research
could make the question of several generations clearer.
The dating of the infilling till units could be based on their
different contents of rounded hornblende grains. The average contents
are: Weichselian (16–25%), Saalian (21–42%) and Elsterian (6–17%)
(Majore et al. 1997). But this analysis is done for the local region and
only several palaeo-incisions have been analyzed. For this reason, this
dating had not been used. The information about contents of rounded
hornblende grains could make it possible to determine the age of
different till units and prove the establishment of several generations
within the palaeo-incisions in the entire area of investigations.
In addition, locally it is rather hard to resolve the changes of
stratigraphic seismic units, the location of palaeo-incisions or other
events such as e.g. gas-saturated rocks, various geological facies and
local irregularities in the sediments by the seismic reflections.
The seismic reflections are often weak in the lowest parts of the
palaeo-incisions, because their infillings are composed in a
complicated way (it finds expression in seismic reflections of
infilling). Thus, to determine the depth of a palaeo-incision may
become a rather tough issue.
The irregular distribution of the seismic lines (Fig. 14)
inadvertently results in different accuracies in the shape and direction
of the palaeo-incisions, also in different details of mapped geological
boundaries and sub-Quaternary surface within the offshore part of the
studied area.
The fragment of Latvian land territory on the sub-Quaternary map
contains no new data and it has been compiled having used the data
from neighboring areas of Lithuania and Latvia offshore. Thus, it may
be regarded as the ‘soft spot’ of this map.
The correlation between the land and offshore palaeo-incision
networks is not established due to lack of data in the shallow waters.
The shape of palaeo-incisions is known from seismic sections,
which often are not perpendicular to the direction of palaeo-incisions.
84
But, this factor seems to affect the horizontal scale of the section but
not the shape.
The difference in thickness together with the heterogeneities in the
Quaternary strata may act as the additional factor, influencing on the
shapes of palaeo-incisions and becoming the agent for their irregular
distribution in the entire area of investigations.
5.2 GEOECOLOGICAL SIGNIFICANCE OF PALAEO-
INCISIONS
Palaeo-incisions are specific geological structures – they cut, as a
rule, into different geological layers. The information, obtained about
morphology and distribution of the palaeo-incisions in the
southeastern Baltic Sea region, shows that often the palaeo-incisions
dissect a part or the entire Quaternary thickness as well as the upper
part of the pre-Quaternary sedimentary bedrock. Thus, if a palaeo-
incision is filled by aqua-glacial sediments with a high permeability,
i.e. sand and gravel, it could be associated with a ‘hydro-geological
window’ between different aquifers. The aquifers are usually
separated by layers of impermeable deposits or rocks, e.g. till, clay,
dolomite, marlstones, etc. Quaternary inter-till sandy horizons,
Cretaceous–Jurassic sand and sandstone and Permian limestone are
associated with main aquifers of fresh groundwater supply in the area
of investigation. Whereas the glacial till and clay separate the
Quaternary aquifers, Cretaceous–Jurassic and Triassic clayey deposits
(confining beds) separate the pre-Quaternary aquifers (Juodkazis
1979). If one or a few aquifers of groundwater supply are presented in
the region of palaeo-incision development, some potential
geoecological risks are possible. During the groundwater extraction,
when the hydrostatic pressure in the particular aquifers falls, vertical
circulation of water between neighboring aquifers might start (or be
significantly intensified) via the above ‘hydro-geological windows’,
i.e. palaeo-incisions. Thus, two possible scenarios of geoecological
risk are available in this case in the southeastern Baltic Sea region:
85
- the groundwater from the upper aquifers, including unconfined
groundwater, might begin to infiltrate into lower horizons. The
unconfined groundwater is not protected from anthropogenic
influence and often contains anthropogenic pollution (fertilizers,
heavy metals, oil products, etc.). In this case polluted water from
unconfined groundwater horizon could infiltrate into the deeper
horizons having used for drinking purposes, as a result of this process
the drinking water could receive a particular dose of the above
pollutants of anthropogenic origin;
- particular aquifers in the pre-Quaternary rock sequence contain
not fresh, but salt water – such water is characteristic of the Permian
and Jurassic aquifers located in the southernmost part of the
investigated area (Juodkazis 1979; Mokrik 2003). During the intensive
drinking water extraction, the salt water located in deeper horizons
might begin to infiltrate into the upper ones (via palaeo-incisions first
of all), reducing the quality of the drinking water.
Another geoecological risk could be related with the distribution of
palaeo-incisions in the bottom of the Southeastern Baltic Sea. As it
has been established during earlier investigations, the palaeo-incisions
are closely connected to zones of tectonic faults (Nechiporenko 1989).
Tectonic activity could stimulate destruction of sediments solidity, i.e.
to form crushing zones along the tectonic faults where more intensive
water circulation might begin (Bitinas 1999, 2011; Satkūnas 2000,
2008). Furthermore, tectonic faults in the pre-Quaternary sedimentary
bedrock are zones where groundwater (including salt water)
discharges. Several zones are described, where salt or fresh
groundwater is discharged at the seafloor of the Southeastern Baltic
Sea, and these zones could be connected to tectonic faults and palaeo-
incisions (Mokrik 2003). The salt/fresh water discharged from the pre-
Quaternary sedimentary bedrock of the Southeastern Baltic Sea is
characterized by different chemical compositions in relation to the
modern Baltic Sea water. The differences in chemical composition of
benthic water (Mokrik 2003) most probably reflect the above tectonic
processes. Thus, the differences in chemical composition of near
bottom water could potentially affect the development of benthic
86
ecosystems, and this is still not an investigated issue of marine biology
and ecology in the southeastern Baltic Sea area. The distribution of
palaeo-incisions might act as a potential indicator for the identification
of submarine groundwater discharge zones.
The palaeo-incisions cut into the Quaternary strata, produce
irregularities in the field of seismic velocities during seismic surveys
both on land and offshore. In case the reason is unknown, the
irregularities of the seismic velocities in the upper part of geological
section might affect the reflections of deeper geological layers,
followed by possible incorrect interpretation of deep seismic data
during planning the well for oil exploration, for example.
The palaeo-incision infills are different as compared to the
enclosing stratal sequences, especially in the cases when the palaeo-
incisions are cut into the pre-Quaternary rocks. Their occurrences are
of dual importance on land. From a hydro-geological point of view,
they are not only ‘hydro-geological windows’, subjected to possible
potential geoecological risks, but are at the same time attractive areas
for fresh groundwater exploration and pumping. This is especially true
when there is a need for major amounts of groundwater for centralized
supply of cities or settlements. On the other hand, the palaeo-incisions
may be regarded as obstacles, which are dissecting the homogenous
sedimentary structures – this fact has a negative significance during
the construction of massive buildings or extraction of different
mineral resources. Thus, it is possible to argue, that the distribution of
the palaeo-incision network in the seafloor of Southeastern Baltic Sea
could be a negative factor from an engineering-geological point of
view, taking into account that this region is perspective of future
marine industry: building oil prospecting and extraction platforms,
wind-power plants, etc.
87
6. CONCLUSIONS
1. Eighty-two fragments of palaeo-incisions have been discovered
by the continuous seismic profiling data digital interpretation in the
southeastern part of the Baltic Sea. They form three separate networks
differentiated by their morphology and depth of the palaeo-incisions.
2. The morphology of the palaeo-incisions changes from the
complicated W- and WW-shape forms near the shore to the simple V-
shape in the western zone. The average width decreases from the
eastern zone (2340 m), through the central zone (1460 m) to the
western zone (960 m). The relative depth of palaeo-incisions increases
from 23–80 m in the eastern zone, through 27–113 m in the central
zone to 53–153 m in the deepwater zone.
3. The newly compiled map of palaeo-incisions on the sub-
Quaternary surface primarily differs from the previous one in the
eastern and in the central zones: the sub-Quaternary relief have been
detailed, and the network of previously unknown fragments of palaeo-
incisions have been discovered and compiled.
4. A new version of the pre-Quaternary geological map of the
investigated area has been compiled. The outcrops of Late Devonian,
Late Permian, Early Triassic, Middle and Late Jurassic, also
Cretaceous sedimentary rocks on the sub-Quaternary surface, have
been contoured more precisely compared to the previously published
maps.
5. Based on the analysis of internal seismic reflectors, seven types
of deposits have been differentiated in infillings of palaeo-incisions in
the entire area of investigations. The particular type of palaeo-incision
infilling was interpreted having used well data: sediments of the
different Pleistocene stages – clay, silt, mud, stratified and unstratified
layers of sand and gravel and three type of till – have been
determined.
6. The integrated geophysical investigation, consisting of 2D CMP
seismic method and electrical tomography survey, makes it partly
88
possible to locate palaeo-incisions and describe their shape and depth
on land. To locate and describe the palaeo-incisions effectively, it is
necessary to append the gravity method to the integrated geophysical
survey, and to test and choose the other electromagnetic method of
deeper penetration.
89
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Geology of Lithuania. Science and encyclopaedia publisher, Vilnius,
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19.
Data sources: Lithuanian Geological Survey database (2014 10 01):
http://www.lgt.lt/zemelap/main.php?sesName=lgt1412160593
The technical parameters of The Upgraded Quartzitic Land
Gravimeter (GNU-KV) (2014 10 01):
http://www.enoutech.com/en/sh_product.asp?cid=46&id=83
EUROSEISMIC project (2014 10 01):
http://www.eu-seased.net: Seismic and sonar/Euroseismic/metaformat
Leibniz Institute for Applied Geophysics (2015 02 04)
http://www.liag-hannover.de/fileadmin/user_upload/dokumente/
Grundwassersysteme/BURVAL/buch/065-076.pdf
100
APPENDIX 1
The catalog of used wells.
Land wells1
Well East North Depth Geology Lithology
Top
depth,
m
573 319326.9 6218493.6 282.5 Q 0
T1 clay 49
P2 limestone 136
C1 marlstone 163.5
D3 dolomite 208
2868 318192.3 6212189.5 251 Q 0
T1 clay 57
P2 limestone 153
C1 marlstone 178
D3 dolomite 228
8592 317605.8 6211521.6 185 Q 0
T1 clay 46
P2 limestone 153
8594 318221.2 6212391.3 250.5 Q 0
T1 clay 60
P2 limestone 150
C1 dolomite 178
1 Lithuanian Geological Survey database (2014 10 01):
http://www.lgt.lt/zemelap/main.php?sesName=lgt1412160593
101
D3 dolomite 232
8634 318201.9 6212280.8 250 Q 0
T1 clay 58
P2 limestone 154
C1 marlstone 176
D3 dolomite 229
9870 317615.4 6207682.4 258 Q 0
T1 clay 54
P2 limestone 178
C1 dolomite 189
D3 dolomite 237
11248 317711.5 6210315.6 300 Q 0
T1
clay,
siltstone 46
P2 limestone 153.5
C1 marlstone 182
D3 dolomite 229
11249 317884.6 6209277.7 90 Q 0
T1 clay 78
19622 318115.4 6216547.6 70 Q 0
T1 clay 51
19623 317970.3 6217088.3 240 Q 0
Table 3
P2 limestone 135
C1 marlstone 162
D3 dolomite 210
19631 318278.9 6212670 270 Q 0
T1 clay 52
P2 limestone 141
102
C1 marlstone 178
D3
dolomite,
limestone 201
19657 318432.7 6212655.6 275 Q 0
T1 clay 62
P2 limestone 143
C1 marlstone 180
D3
dolomite,
limestone 233
20084 317663.5 6215610.6 233 Q 0
T1 clay 48
P2 limestone 132
C1 marlstone 158
D3 dolomite 207
25027 319480.8 6216355.4 148 Q 0
P2 limestone 136
25513 318884.6 6208177.3 254 Q 0
T1 clay 97
P2 limestone 171
C1 dolomite 196
D3 dolomite 237
25992 319413.5 6217508.6 240 Q 0
T1 clay 53
P2 limestone 132
C1 marlstone 158
D3 dolomite 213
25993 319403.9 6217326 238 Q 0
T1 clay 53
103
P2 limestone 132
C1 marlstone 159
D3 dolomite 213
36225 317567.3 6217282.7 116 Q 0
Deep offshore wells2
Well East North Depth Geology Lithology
Top
depth,
m
D5 290425.8 6161089.6 2367 Water 0
Fig. 24; Fig. 16
Q 62
J3 clay 90
J2 marlstone 107
T1
clay,
siltstone,
sandstone 154
P2
limestone,
dolomite 358
D3
dolomite,
sandstone 438
D6 284277.4 6140296.2 2396 Water 0
Fig. 17
Q 30
K2 sandstone 48
J3 clay 144
J2 marlstone 203
T1
clay,
siltstone,
sandstone 239
2 Grigelis 1991
104
P2
limestone,
dolomite,
anhydrite 519
D3
dolomite,
sandstone 643
E6 277686.4 6245927.2 1095 Water 0
Fig. 18
Q 36.5
D3
dolomite,
sandstone 38
D2
clay,
siltstone,
sandstone 145
E7 232694.7 6216139.4 1651 Water 0
Fig. 19
Q 53
D3
dolomite,
sandstone 54
D2
clay,
siltstone,
sandstone 214
Shallow offshore wells3
Well East North Depth Geology Lithology
Top
depth,
m
591 314176.1 6218052 11 Q 0
54M 277791.2 6171882.5 47 Q 0
Fig. 30 bedrock 46
55M 256823.8 6194568.5 30 Q 0
56M 250952.8 6211893.5 30 Q 0
bedrock 28
3 Majore et al. 1997; Gelumbauskaitė 2009.
105
58M 251411.9 6181497.5 74 Q 0
Fig. 32
59M 299475.7 6175613 25 Q 0
bedrock 23
60M 305246.5 6183912.5 12 Q 0
bedrock 11
61M 266471.3 6188127.5 23 Q 0
71M 283508.4 6195324.5 39 Q 0
bedrock 38
D11-1P 299694.8 6213686 30 Q 0
Fig. 33 bedrock 29
D26-1P 292991.5 6179827.5 15 Q 0
bedrock 14
D5-1/1P 295974.7 6154181.8 30 Q 0
bedrock 28
E7-1/2P 240430.8 6218877 2 Q 0
bedrock 1
106
APPENDIX 2.
The coordinates of CSP seismic lines.
Line Start of line End of line Length,
km Lat N Long E Lat N Long E
9302B 55˚ 15.9’ 20˚ 21.0’ 55˚ 23.3’ 20˚ 42.2’ 26.4
9404 56˚ 20.0’ 20˚ 40.0’ 55˚ 18.5’ 20˚ 39.7’ 114.2
9405 55˚ 18.7’ 20˚ 49.9’ 56˚ 21.7’ 20˚ 50.1’ 116.9
9410A 56˚ 22.9’ 20˚ 45.0’ 56˚ 00.9’ 20˚ 45.1’ 40.8
9410B 55˚ 57.3’ 20˚ 45.0’ 55˚ 24.9’ 20˚ 45.0’ 60.0
9513 56˚ 09.9’ 20˚ 50.5’ 55˚ 44.1’ 19˚ 35.3’ 91.8
9514 55˚ 41.5’ 19˚ 43.0’ 55˚ 60.0’ 20˚ 35.0’ 64.2
9515 55˚ 50.0’ 20˚ 27.5’ 55˚ 30.0’ 20˚ 27.5’ 37.0
9516 55˚ 30.0’ 20˚ 25.0’ 55˚ 50.0’ 20˚ 25.0’ 37.1
9517 55˚ 50.0’ 20˚ 22.6’ 55˚ 30.0’ 20˚ 22.5’ 37.2
9518 55˚ 30.1’ 20˚ 17.5’ 55˚ 50.0’ 20˚ 17.5’ 37.0
9520 55˚ 30.0’ 20˚ 12.5’ 55˚ 50.0’ 20˚ 12.5’ 37.0
9521 55˚ 46.6’ 20˚ 07.5’ 55˚ 30.0’ 20˚ 07.5’ 30.8
9522 55˚ 30.0’ 20˚ 05.0’ 55˚ 50.0’ 20˚ 05.0’ 37.1
9523 55˚ 50.0’ 20˚ 02.5’ 55˚ 30.0’ 20˚ 02.5’ 37.0
9524 55˚ 30.0’ 19˚ 57.5’ 55˚ 50.0’ 19˚ 57.5’ 37.1
9525 55˚ 50.0’ 19˚ 55.0’ 55˚ 37.0’ 19˚ 55.0’ 24.2
9526A 55˚ 35.0’ 19˚ 59.9’ 55˚ 35.0’ 20˚ 32.5’ 34.2
9526B 55˚ 45.0’ 20˚ 32.5’ 55˚ 45.0’ 19˚ 45.0’ 49.7
980829_3 56˚ 22.7’ 20˚ 35.0’ 55˚ 40.0’ 20˚ 35.0’ 79.3
980829_4 55˚ 40.0’ 20˚ 35.0’ 55˚ 26.9’ 20˚ 34.5’ 24.4
980830_1 55˚ 30.4’ 20˚ 25.0’ 56˚ 05.9’ 20˚ 25.0’ 65.8
107
980830_3A 56˚ 07.8’ 20˚ 25.4’ 56˚ 08.2’ 20˚ 25.0’ 0.9
980830_3B 56˚ 08.9’ 20˚ 25.0’ 56˚ 10.0’ 20˚ 25.0’ 2.0
980830_5A 56˚ 10.3’ 20˚ 25.0’ 56˚ 18.9’ 20˚ 25.0’ 15.9
980830_5B 56˚ 20.0’ 20˚ 21.9’ 56˚ 20.1’ 20˚ 10.2’ 12.1
980830_5C 56˚ 18.2’ 20˚ 05.1’ 55˚ 43.7’ 20˚ 05.0’ 64.0
980830_6A 55˚ 42.0’ 20˚ 04.7’ 55˚ 38.0’ 20˚ 05.0’ 7.3
980830_6B 55˚ 36.7’ 20˚ 06.0’ 55˚ 33.5’ 20˚ 13.8’ 10.2
980830_6C 55˚ 33.8’ 20˚ 15.0’ 56˚ 22.4’ 20˚ 15.0’ 90.2
980901_1 56˚ 21.9’ 19˚ 55.0’ 56˚ 04.7’ 19˚ 54.9’ 31.9
980901_2A 56˚ 04.4’ 19˚ 54.7’ 55˚ 40.5’ 19˚ 55.0’ 44.5
980901_2B 55˚ 40.3’ 19˚ 54.0’ 55˚ 41.7’ 19˚ 49.1’ 5.8
980901_3 55˚ 44.3’ 19˚ 45.0’ 56˚ 19.5’ 19˚ 45.0’ 65.3
980901_4A 56˚ 19.7’ 19˚ 25.0’ 55˚ 49.1’ 19˚ 26.6’ 56.8
980901_4B 55˚ 52.0’ 19˚ 35.0’ 56˚ 19.9’ 19˚ 35.0’ 51.8
980901_6 56˚ 18.7’ 19˚ 15.1’ 55˚ 56.0’ 19˚ 15.0’ 42.1
980903_1 55˚ 57.0’ 19˚ 05.0’ 55˚ 58.7’ 19˚ 05.0’ 3.2
980903_2 55˚ 58.9’ 19˚ 05.0’ 56˚ 17.5’ 19˚ 05.0’ 34.5
990818_2 56˚ 00.0’ 18˚ 49.3’ 55˚ 37.1’ 20˚ 03.2’ 88.2
990818_3A 55˚ 37.1’ 20˚ 03.3’ 55˚ 40.1’ 20˚ 22.6’ 21.1
990818_3B 55˚ 41.4’ 20˚ 23.8’ 55˚ 49.9’ 19˚ 58.6’ 30.7
990818_3C 55˚ 48.8’ 19˚ 56.0’ 55˚ 38.6’ 20˚ 25.4’ 36.1
990819_1A 55˚ 38.0’ 20˚ 27.3’ 55˚ 37.4’ 20˚ 28.8’ 1.8
990819_1B 55˚ 36.0’ 20˚ 29.8’ 55˚ 47.4’ 19˚ 54.3’ 42.7
990819_2 55˚ 46.6’ 19˚ 51.8’ 55˚ 38.9’ 20˚ 15.0’ 28.2
990820_1A 55˚ 37.5’ 20˚ 19.2’ 55˚ 35.7’ 20˚ 24.5’ 6.5
990820_1B 55˚ 34.3’ 20˚ 24.0’ 55˚ 45.8’ 19˚ 49.1’ 42.3
990820_1C 55˚ 44.9’ 19˚ 47.5’ 55˚ 39.8’ 20˚ 03.1’ 18.9
990821_1A 55˚ 39.4’ 19˚ 59.3’ 55˚ 43.9’ 19˚ 44.9’ 17.3
108
990821_1B 55˚ 43.4’ 19˚ 44.6’ 55˚ 32.1’ 20˚ 47.0’ 68.9
990821_1C 55˚ 34.1’ 20˚ 46.8’ 55˚ 37.7’ 20˚ 36.9’ 12.3
990821_2D 55˚ 37.7’ 20˚ 36.9’ 55˚ 38.0’ 20˚ 36.1’ 1.0
990821_3A 55˚ 38.6’ 20˚ 36.0’ 55˚ 48.2’ 20˚ 36.0’ 17.8
990821_3B 55˚ 49.3’ 20˚ 36.6’ 55˚ 55.5’ 20˚ 53.6’ 21.2
990821_3C 55˚ 56.2’ 20˚ 54.1’ 55˚ 59.6’ 20˚ 12.5’ 43.8
990821_3D 56˚ 00.3’ 20˚ 09.4’ 56˚ 00.1’ 20˚ 04.9’ 4.7
990821_4A 56˚ 00.0’ 20˚ 05.0’ 55˚ 50.8’ 20˚ 23.5’ 25.8
990821_4B 55˚ 50.0’ 20˚ 23.4’ 55˚ 50.0’ 20˚ 17.5’ 6.2
990821_4C 55˚ 50.5’ 20˚ 14.1’ 55˚ 58.7’ 19˚ 59.4’ 21.5
990822_1 56˚ 00.0’ 19˚ 54.0’ 56˚ 01.5’ 19˚ 45.7’ 9.0
990822_2 56˚ 09.7’ 19˚ 01.0’ 56˚ 10.0’ 18˚ 51.9’ 9.5
Total: 2233.1
109
AP
PE
ND
IX 3
.
The
coord
inat
es a
nd t
he
shap
e of
pal
aeo
-in
cisi
ons,
als
o t
hic
knes
s of
infi
lled
sei
smic
un
its.
E
ncl
osi
ng
seis
mo
stra
ti-
gra
ph
ic u
nit
s
Th
e ce
nte
r o
f
pa
laeo
-in
cisi
on
Shape
Th
ick
nes
s o
f in
fill
ed s
eism
ic u
nit
, m
No
. L
at,
N
Lo
ng
, E
A
A
21
B
C
D
E
F
G
Infi
llin
g,
m
1
D3
5
6˚
14
.6’
19
˚ 05
.0’
V
10
.8 1
5.3
25
.2 4
2.3
93
.6
Western zone
2
D3
5
6˚
13
.5’
19
˚ 15
.1’
V
1
7.1
14
.4 2
1.6
25
.2 2
9.7
10
8.0
3
D3
5
6˚
10
.0’
18
˚ 54
.1’
V
14
.4
7
.2
18
.0 1
6.2
55
.8
4
D3
5
6˚
09
.1’
19
˚ 15
.1’
V
18
.9
9.9
1
6.2
27
.0 4
5.9
11
7.9
5
D3
5
6˚
06
.4’
19
˚ 05
.0’
V
17
.1
10
.8 4
7.7
22
.5 3
1.5
12
9.6
6
D3
5
6˚
04
.0’
19
˚ 25
.0’
W
1
5.3
9.0
9
.0
30
.6 4
5.0
10
8.9
7
D3
5
6˚
02
.4’
19
˚ 25
.0’
U
2
1.6
7.2
1
0.8
21
.6 3
5.1
96
.3
8
D3
(F
ig.
30
A)
56
˚ 01
.2’
19
˚ 05
.0’
V
19
.8 1
0.8
13
.5 2
8.8
25
.2 2
9.7
12
7.8
9
D3
5
5˚
57
.9’
19
˚ 03
.4’
V
25
.2
1
2.6
18
.0 2
7.0
29
.7 3
0.6
14
3.1
10
D3
5
5˚
53
.1’
19
˚ 12
.3’
W
9.9
2
7.0
3
2.4
39
.6 2
2.5
13
1.4
11
D3
5
5˚
56
.0’
19
˚ 06
.4’
V
29
.7 9
.9
20
.7 5
.4
7.2
72
.9
1 – t
he
sam
e as
Unit
A, bu
t dee
per
.
110
1
2
P2
56
˚ 17
.7’
20
˚ 50
.1’
V
3.6
5.4
7
.2
11
.7
27
.9
Eastern zone 1
3
P2
56
˚ 13
.6’
20
˚ 50
.0’
U
6.3
5.4
9
.0
12
.6
33
.3
14
P2
, T
1
(F
ig.
34
) 5
6˚
02
.1’
20
˚ 50
.0’
W
6.3
9
.0
18
.9
34
.2
15
P2
, T
1
56
˚ 16
.7’
20
˚ 45
.1’
V
8.1
2
0.7
31
.5
16
P2
, T
1
56
˚ 10
.6’
20
˚ 45
.0’
V
7.2
9.0
2
2.5
22
.5
61
.2
17
P2
, T
1
56
˚ 09
.7’
20
˚ 45
.0’
V
9.0
9.0
2
1.6
18
.0
57
.6
18
T1,
J2
56
˚ 05
.5’
20
˚ 45
.0’
WW
10
.8 9
.0
16
.2 1
8.0
18
.0 7
2.0
19
T1,
J2
56
˚ 03
.5’
20
˚ 45
.0’
W
12
.6
7
.2
1
6.2
16
.2 2
1.6
73
.8
20
P2
, T
1
56
˚ 16
.4’
20
˚ 40
.0’
W
1
3.5
1
8.9
23
.4 9
.0
64
.8
21
P2
, T
1
56
˚ 08
.9’
20
˚ 40
.0’
W
7.2
7
.2
1
4.4
1
0.8
11
.7 2
0.7
72
.0
22
P2
, T
1
56
˚ 07
.6’
20
˚ 40
.0’
W
7.2
1
1.7
2
7.9
12
.6 1
5.3
74
.7
23
P2
, T
1
56
˚ 06
.8’
20
˚ 40
.0’
W
5.4
1
0.8
2
6.1
11
.7 7
.2
61
.2
24
P2
, T
1
56
˚ 05
.2’
20
˚ 40
.0’
U
9.9
6
.3
1
8.0
13
.5 1
7.1
64
.8
25
P2
, T
1
56
˚ 02
.6’
20
˚ 40
.0’
W
7.2
1
0.8
2
3.4
6.3
47
.7
26
P2
, T
1
56
˚ 17
.2’
20
˚ 35
.0’
W
8.1
1
1.7
17
.1 1
8.9
7.2
2
6.1
89
.1
27
P2
, T
1
(Fig
. 3
0E
) 5
6˚
09
.1’
20
˚ 35
.0’
W
14
.4 1
2.6
16
.2 1
5.3
5.4
2
3.4
87
.3
28
T1,
J2, J3
5
5˚
45
.7’
20
˚ 50
.0’
V
2.7
1
5.3
10
.8
28
.8
29
T1,
J2, J3
5
5˚
40
.1’
20
˚ 50
.0’
WW
5
.4
12
.6 1
2.6
3
0.6
111
30
T1,
J2, J3
5
5˚
35
.9’
20
˚ 50
.0’
WW
5
.4
13
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4.4
3
3.3
31
P2
, T
1, J
2,
J3
(Fig
. 3
0F
) 5
5˚
31
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20
˚ 50
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WW
7
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12
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1.6
27
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9.3
32
J2, J3
5
5˚
23
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20
˚ 50
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WW
5
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14
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3.4
4
3.2
33
T1
(F
ig.
30
G)
55
˚ 47
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20
˚ 45
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WW
6
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9.9
11
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1.7
18
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8.5
34
T1,
J2, J3
5
5˚
37
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20
˚ 45
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U
1
2.6
21
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8.8
63
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35
J2, J3
5
5˚
36
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20
˚ 45
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V
3
0.6
30
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36
T1,
J2, J3
5
5˚
31
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20
˚ 45
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V
2
3.4
25
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48
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37
T1,
J2, J3
5
5˚
26
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20
˚ 45
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W
2
1.6
32
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54
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38
T1,
J2, J3
5
5˚
36
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20
˚ 40
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W
1
6.2
40
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56
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39
T1,
J2, J3
5
5˚
31
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20
˚ 40
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U
1
5.3
18
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34
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40
J2, J3
5
5˚
30
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20
˚ 35
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U
4
2.3
42
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41
T1,
J2, J3
5
5˚
36
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20
˚ 35
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U
12
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12
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6.2
30
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89
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42
T1
55
˚ 58
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20
˚ 41
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W
16
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17
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2.5
14
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70
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43
T1
55
˚ 53
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20
˚ 48
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V
12
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1
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25
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1.7
64
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44
J2, J3
5
5˚
30
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20
˚ 39
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V
2
0.7
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43
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45
T1,
J2, J3
5
5˚
35
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20
˚ 44
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U
3
6.9
36
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46
T1,
J2, J3
5
5˚
36
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20
˚ 40
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V
3
3.3
33
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47
T1,
J2, J3
5
5˚
37
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20
˚ 38
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W
2
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25
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112
48
P2
55
˚ 52
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19
˚ 45
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W
6.3
1
2.6
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7
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35
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Central zone 4
9
P2
, T
1
55
˚ 47
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19
˚ 45
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W
1
2.6
15
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27
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50
T1
55
˚ 45
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19
˚ 45
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V
6
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10
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17
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51
D3
5
6˚
05
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19
˚ 55
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V
7.2
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13
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9.8
9.9
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91
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D3
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2
55
˚ 56
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19
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U
7.2
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53
P2
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1
55
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19
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W
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24
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54
P2
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55
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T1,
J2
55
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20
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56
T1,
J2
55
˚ 49
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20
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1
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57
T1,
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55
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20
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7
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71
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58
T1,
J2
55
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20
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8
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1
8.9
24
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71
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59
T1,
J2, J3
5
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37
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20
˚ 15
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9.9
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0.7
31
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60
T1,
J2, J3
5
5˚
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20
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12
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8.0
23
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7.1
71
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61
T1,
J2, J3
5
5˚
40
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20
˚ 25
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V
6.3
11
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1.7
20
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67
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62
T1,
J2, J3
5
5˚
37
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20
˚ 25
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V
9.0
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8.9
31
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8.9
90
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63
T1
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2,
J3
(Fig
. 3
2)
55
˚ 32
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20
˚ 25
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V
1
1.7
14
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3.5
18
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57
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64
T1,
J2, J3
5
5˚
36
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20
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U
10
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34
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61
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65
P2
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1
55
˚ 46
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19
˚ 41
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9.9
9
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5.3
58
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66
P2
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1
55
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19
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1
0.8
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67
P2
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1
55
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19
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W
11
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2
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64
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68
P2
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1, J
2
(Fig
. 3
0D
) 5
5˚
54
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20
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V
8.1
4
2.3
22
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6.1
99
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69
P2
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1, J2
, J3
5
5˚
42
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19
˚ 45
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V
13
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12
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8.9
54
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70
T1,
J2
55
˚ 50
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20
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W
6.3
9.0
1
3.5
15
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44
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71
T1,
J2
55
˚ 52
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20
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U
6.3
10
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2
4.3
17
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2.6
71
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72
P2
, T
1
55
˚ 53
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20
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U
7.2
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2
2.5
24
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0.8
73
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73
T1
55
˚ 51
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20
˚ 21
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V
2
3.4
25
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1.6
70
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74
P2
, T
1
55
˚ 53
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20
˚ 17
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V
7.2
9.0
2
2.5
24
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0.8
73
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75
D3
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2, T
1
55
˚ 57
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20
˚ 00
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V
9
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1
4.4
10
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4.4
49
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76
T1,
J2
55
˚ 54
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20
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W
19
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5.3
2
7.9
21
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10
2.6
77
T1,
J2
55
˚ 45
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20
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U
10
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1
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21
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3.3
91
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78
P2
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1, J2
5
5˚
45
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20
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V
9.9
11
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35
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10
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79
T1,
J2
55
˚ 45
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20
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W
9.0
11
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44
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5.2
10
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80
T1,
J2, J3
5
5˚
35
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20
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V
6.3
8
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18
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6.2
49
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81
J2, J3
5
5˚
35
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20
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W
1
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6
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18
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42
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82
J2, J3
5
5˚
35
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20
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U
11
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1
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19
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46
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83
J2, J3
5
5˚
35
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20
˚ 30
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W
9.9
1
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23
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50
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84
T1,
J2, J3
5
5˚
41
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19
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V
11
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14
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18
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1.6
90
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114
85
T1,
J2, J3
5
5˚
42
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19
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U
12
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18
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94
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86
T1
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2,
J3
(Fig
. 3
3)
55
˚ 42
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20
˚ 02
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V
12
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11
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3.3
18
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8.9
94
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87
T1,
J2, J3
5
5˚
37
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20
˚ 07
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W
16
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1.7
24
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5.3
67
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88
T1,
J2, J3
5
5˚
36
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20
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U
9.9
1
8.0
19
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4.3
72
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89
T1,
J2, J3
5
5˚
38
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20
˚ 12
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V
11
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0.8
46
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0.7
90
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90
T1,
J2, J3
5
5˚
42
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20
˚ 12
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U
14
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36
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2.5
90
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91
T1,
J2
55
˚ 46
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20
˚ 12
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V
11
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11
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0.8
10
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1.6
66
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92
T1
55
˚ 49
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20
˚ 12
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U
8.1
13
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16
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47
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93
T1,
J2, J3
5
5˚
37
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20
˚ 22
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U
19
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1.7
6.3
1
6.2
14
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4.3
92
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94
P2
, T
1, J2
5
5˚
46
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20
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V
15
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3.5
10
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10
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2.5
97
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95
P2
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1, J2
5
5˚
48
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20
˚ 01
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W
15
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2.6
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2
7.0
11
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1.6
97
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96
D3
-J3
(Fig
. 3
0B
) 5
5˚
43
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19
˚ 42
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V
8.1
2
0.7
16
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6.1
71
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97
D3
-J3
5
5˚
42
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19
˚ 46
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U
14
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3.4
18
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2.5
78
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98
D3
-J3
5
5˚
41
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19
˚ 50
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U
17
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0.8
20
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0.7
37
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2.5
12
9.6
99
T1,
J2, J3
5
5˚
40
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19
˚ 52
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V
23
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1.7
18
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12
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7.9
10
3.5
10
0
T1,
J2, J3
5
5˚
38
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19
˚ 59
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V
9.0
1
4.4
26
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1.7
9.9
2
7.0
98
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10
1
D3
(F
ig.
30
H)
56
˚ 02
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20
˚ 04
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V
10
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6.3
1
1.7
1
4.4
14
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64
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10
2
T1
, J
2
(Fig
. 3
0C
) 5
5˚
43
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20
˚ 04
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U
9.9
9
19
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17
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4.2
12
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02
.6